diff --git a/src/backend/mir_interpreter/handlers/boxes_object_fields.rs b/src/backend/mir_interpreter/handlers/boxes_object_fields.rs
index ca50fbf1..4c0d9fe2 100644
--- a/src/backend/mir_interpreter/handlers/boxes_object_fields.rs
+++ b/src/backend/mir_interpreter/handlers/boxes_object_fields.rs
@@ -41,7 +41,7 @@ pub(super) fn try_handle_object_fields(
             // Static box support: if box_val is a string matching a static box name,
             // resolve it to the singleton instance
             let actual_box_val = if let Ok(VMValue::String(ref box_name)) = this.reg_load(box_val) {
-                if this.static_box_decls.contains_key(box_name) {
+                if this.static_box_registry.exists(box_name) {
                     // Get or create singleton instance
                     let instance = this.ensure_static_box_instance(box_name)?;
                     let instance_clone = instance.clone();
@@ -363,7 +363,7 @@ pub(super) fn try_handle_object_fields(
             // Static box support: if box_val is a string matching a static box name,
             // resolve it to the singleton instance
             let actual_box_val = if let Ok(VMValue::String(ref box_name)) = this.reg_load(box_val) {
-                if this.static_box_decls.contains_key(box_name) {
+                if this.static_box_registry.exists(box_name) {
                     // Get or create singleton instance
                     let instance = this.ensure_static_box_instance(box_name)?;
                     let instance_clone = instance.clone();
diff --git a/src/backend/mir_interpreter/handlers/calls/method.rs b/src/backend/mir_interpreter/handlers/calls/method.rs
index 4c46fddd..d2673d41 100644
--- a/src/backend/mir_interpreter/handlers/calls/method.rs
+++ b/src/backend/mir_interpreter/handlers/calls/method.rs
@@ -137,7 +137,7 @@ impl MirInterpreter {
             Ok(out)
         } else {
             // Receiver not provided: try static singleton instance for the box (methodize PoC fallback)
-            if self.static_box_decls.contains_key(box_name) {
+            if self.static_box_registry.exists(box_name) {
                 // 🎯 Phase 173-B: Static box methods are in MIR function table
                 // Try calling the MIR function directly (BoxName.method/arity pattern)
                 let func_name = format!("{}.{}/{}", box_name, method, args.len());
diff --git a/src/backend/mir_interpreter/mod.rs b/src/backend/mir_interpreter/mod.rs
index ce4622d4..587a6deb 100644
--- a/src/backend/mir_interpreter/mod.rs
+++ b/src/backend/mir_interpreter/mod.rs
@@ -21,8 +21,11 @@ mod exec;
 mod handlers;
 mod helpers;
 mod method_router;
+pub mod static_box_registry;
 mod utils;
 
+pub use static_box_registry::StaticBoxRegistry;
+
 pub struct MirInterpreter {
     pub(super) regs: HashMap<ValueId, VMValue>,
     pub(super) mem: HashMap<ValueId, VMValue>,
@@ -34,10 +37,8 @@ pub struct MirInterpreter {
     pub(super) last_block: Option<BasicBlockId>,
     pub(super) last_inst: Option<MirInstruction>,
     pub(super) last_inst_index: Option<usize>,
-    // Static box singleton instances (persistent across method calls)
-    pub(super) static_boxes: HashMap<String, crate::instance_v2::InstanceBox>,
-    // Static box declarations (metadata for creating instances)
-    pub(super) static_box_decls: HashMap<String, crate::core::model::BoxDeclaration>,
+    // 🎯 Phase 173-B: Unified static box management via StaticBoxRegistry
+    pub(super) static_box_registry: StaticBoxRegistry,
     // Lightweight dev counters (opt-in print via NYASH_VM_STATS=1)
     pub(super) inst_count: u64,
     pub(super) branch_count: u64,
@@ -58,8 +59,7 @@ impl MirInterpreter {
             last_block: None,
             last_inst: None,
             last_inst_index: None,
-            static_boxes: HashMap::new(),
-            static_box_decls: HashMap::new(),
+            static_box_registry: StaticBoxRegistry::new(),
             inst_count: 0,
             branch_count: 0,
             compare_count: 0,
@@ -73,17 +73,26 @@ impl MirInterpreter {
     }
 
     /// Register static box declarations (called from vm.rs during setup)
+    /// Now delegated to StaticBoxRegistry
     pub fn register_static_box_decl(
         &mut self,
         name: String,
         decl: crate::core::model::BoxDeclaration,
     ) {
-        self.static_box_decls.insert(name, decl);
+        self.static_box_registry.register_declaration(name, decl);
     }
 
     /// Check if a static box is already registered (Phase 173-B)
+    /// Now delegated to StaticBoxRegistry
     pub fn has_static_box_decl(&self, name: &str) -> bool {
-        self.static_box_decls.contains_key(name)
+        self.static_box_registry.exists(name)
+    }
+
+    /// Initialize registry from MIR function names (auto-detect using imports)
+    /// Called from vm.rs after module is loaded
+    pub fn detect_static_boxes_from_functions(&mut self) {
+        self.static_box_registry
+            .detect_from_mir_functions(self.functions.keys());
     }
 
     /// Execute a BoxCall with VM's complete semantics (Phase 27-shortterm S-5.2-improved)
@@ -153,60 +162,23 @@ impl MirInterpreter {
 
     /// Ensure static box singleton instance exists, create if not
     /// Returns mutable reference to the singleton instance
+    /// Now delegated to StaticBoxRegistry
     fn ensure_static_box_instance(
         &mut self,
         box_name: &str,
     ) -> Result<&mut crate::instance_v2::InstanceBox, VMError> {
-        // Check if instance already exists
-        if !self.static_boxes.contains_key(box_name) {
-            // Get declaration
-            let decl = self
-                .static_box_decls
-                .get(box_name)
-                .ok_or_else(|| {
-                    VMError::InvalidInstruction(format!(
-                        "static box declaration not found: {}",
-                        box_name
-                    ))
-                })?
-                .clone();
-
-            // Create instance from declaration
-            let instance = crate::instance_v2::InstanceBox::from_declaration(
-                box_name.to_string(),
-                decl.fields.clone(),
-                decl.methods.clone(),
-            );
-
-            self.static_boxes.insert(box_name.to_string(), instance);
-
-            if std::env::var("NYASH_VM_STATIC_TRACE").ok().as_deref() == Some("1") {
-                eprintln!(
-                    "[vm-static] created singleton instance for static box: {}",
-                    box_name
-                );
-            }
-        }
-
-        // Return mutable reference
-        self.static_boxes.get_mut(box_name).ok_or_else(|| {
-            VMError::InvalidInstruction(format!(
-                "static box instance not found after creation: {}",
-                box_name
-            ))
-        })
+        self.static_box_registry
+            .get_or_create_instance(box_name)
+            .map_err(|e| VMError::InvalidInstruction(e))
     }
 
     /// Check if a function name represents a static box method
     /// Format: "BoxName.method/Arity"
+    /// Now uses StaticBoxRegistry naming utilities
     #[allow(dead_code)]
     fn is_static_box_method(&self, func_name: &str) -> Option<String> {
-        if let Some((box_name, _rest)) = func_name.split_once('.') {
-            if self.static_box_decls.contains_key(box_name) {
-                return Some(box_name.to_string());
-            }
-        }
-        None
+        static_box_registry::naming::extract_box_name(func_name)
+            .filter(|name| self.static_box_registry.exists(name))
     }
 
     /// Execute module entry (main) and return boxed result
@@ -214,6 +186,10 @@ impl MirInterpreter {
         // Snapshot functions for call resolution
         self.functions = module.functions.clone();
 
+        // 🎯 Phase 173-B: Auto-detect static boxes from MIR function names
+        // This handles using-imported static boxes that aren't in AST
+        self.detect_static_boxes_from_functions();
+
         // Determine entry function with sensible fallbacks
         // Priority:
         //   1) NYASH_ENTRY env (exact), then basename before '/' if provided (e.g., "Main.main/0" → "Main.main")
diff --git a/src/backend/mir_interpreter/static_box_registry.rs b/src/backend/mir_interpreter/static_box_registry.rs
new file mode 100644
index 00000000..c23d3219
--- /dev/null
+++ b/src/backend/mir_interpreter/static_box_registry.rs
@@ -0,0 +1,284 @@
+/*!
+ * StaticBoxRegistry - 静的Box管理の一元化箱
+ *
+ * 箱理論の実践:
+ * - 箱にする: static_box_decls + static_boxes + MIR関数検出を1箱に集約
+ * - 境界を作る: 静的Boxの存在証明・シングルトン管理を単一責務に
+ * - Fail-Fast: 存在しないBoxへのアクセスは即座にエラー
+ *
+ * 設計原則:
+ * - MIR関数名から自動検出: "BoxName.method/arity" パターンでusing importも対応
+ * - 遅延シングルトン: 実際にアクセスされるまでインスタンス作成しない
+ * - 明示的登録も可能: AST経由のBoxDeclarationも受け入れ
+ */
+
+use std::collections::{HashMap, HashSet};
+
+use crate::core::model::BoxDeclaration;
+use crate::instance_v2::InstanceBox;
+
+/// 静的Box管理の一元化レジストリ
+///
+/// Phase 173-B で発生した問題を根本解決:
+/// - using import された静的Boxが static_box_decls に登録されない問題
+/// - MIR関数テーブルと static_box_decls の不整合問題
+pub struct StaticBoxRegistry {
+    /// 明示的に登録されたBoxDeclaration (AST経由)
+    declarations: HashMap<String, BoxDeclaration>,
+
+    /// MIR関数名から検出された静的Box名
+    /// (using import でも自動検出可能)
+    detected_boxes: HashSet<String>,
+
+    /// 実行時シングルトン (遅延作成)
+    instances: HashMap<String, InstanceBox>,
+}
+
+/// MIR関数名のパースユーティリティ
+pub mod naming {
+    /// "BoxName.method/arity" 形式の関数名をパース
+    /// Returns: Some((box_name, method, arity)) or None
+    pub fn parse_static_method_name(fn_name: &str) -> Option<(String, String, usize)> {
+        // "BoxName.method/arity" or "BoxName.method"
+        let dot_pos = fn_name.find('.')?;
+        let box_name = &fn_name[..dot_pos];
+        let rest = &fn_name[dot_pos + 1..];
+
+        let (method, arity) = if let Some(slash_pos) = rest.find('/') {
+            let method = &rest[..slash_pos];
+            let arity_str = &rest[slash_pos + 1..];
+            let arity = arity_str.parse::<usize>().ok()?;
+            (method.to_string(), arity)
+        } else {
+            (rest.to_string(), 0)
+        };
+
+        Some((box_name.to_string(), method, arity))
+    }
+
+    /// 静的Boxメソッド名を生成
+    pub fn static_method_name(box_name: &str, method: &str, arity: usize) -> String {
+        format!("{}.{}/{}", box_name, method, arity)
+    }
+
+    /// 関数名からBox名を抽出 (メソッド・arity無視)
+    pub fn extract_box_name(fn_name: &str) -> Option<String> {
+        parse_static_method_name(fn_name).map(|(box_name, _, _)| box_name)
+    }
+}
+
+/// 除外する組み込みBox名 (静的Boxではない)
+const BUILTIN_RUNTIME_BOXES: &[&str] = &[
+    "Main",
+    "main",
+    "StringBox",
+    "IntegerBox",
+    "BoolBox",
+    "ArrayBox",
+    "MapBox",
+    "FloatBox",
+    "VoidBox",
+    "NullBox",
+    "ConsoleBox",
+    "MathBox",
+    "FileBox",
+    "NetBox",
+    "CounterBox",
+];
+
+impl StaticBoxRegistry {
+    /// 空のレジストリを作成
+    pub fn new() -> Self {
+        Self {
+            declarations: HashMap::new(),
+            detected_boxes: HashSet::new(),
+            instances: HashMap::new(),
+        }
+    }
+
+    /// MIR関数名一覧から静的Boxを自動検出
+    ///
+    /// using import された静的Boxも含めて検出可能
+    pub fn detect_from_mir_functions<'a, I>(&mut self, fn_names: I)
+    where
+        I: Iterator<Item = &'a String>,
+    {
+        for fn_name in fn_names {
+            if let Some(box_name) = naming::extract_box_name(fn_name) {
+                // 組み込みランタイムBoxは除外
+                if !BUILTIN_RUNTIME_BOXES.contains(&box_name.as_str()) {
+                    self.detected_boxes.insert(box_name);
+                }
+            }
+        }
+
+        if std::env::var("NYASH_STATIC_BOX_REGISTRY_TRACE")
+            .ok()
+            .as_deref()
+            == Some("1")
+        {
+            eprintln!(
+                "[static-box-registry] detected {} static boxes from MIR functions",
+                self.detected_boxes.len()
+            );
+            for name in &self.detected_boxes {
+                eprintln!("  - {}", name);
+            }
+        }
+    }
+
+    /// BoxDeclarationを明示的に登録 (AST経由)
+    pub fn register_declaration(&mut self, name: String, decl: BoxDeclaration) {
+        self.declarations.insert(name, decl);
+    }
+
+    /// 静的Boxが存在するか確認
+    ///
+    /// 以下のいずれかで存在とみなす:
+    /// 1. declarations に登録済み
+    /// 2. detected_boxes に検出済み
+    pub fn exists(&self, name: &str) -> bool {
+        self.declarations.contains_key(name) || self.detected_boxes.contains(name)
+    }
+
+    /// シングルトンインスタンスを取得または作成
+    ///
+    /// 遅延作成: 初回アクセス時にのみ作成
+    pub fn get_or_create_instance(&mut self, name: &str) -> Result<&mut InstanceBox, String> {
+        if !self.exists(name) {
+            return Err(format!(
+                "static box '{}' not found in registry (neither declared nor detected)",
+                name
+            ));
+        }
+
+        // 既存インスタンスがあればそれを返す
+        if self.instances.contains_key(name) {
+            return Ok(self.instances.get_mut(name).unwrap());
+        }
+
+        // 新規作成
+        let instance = if let Some(decl) = self.declarations.get(name) {
+            // 明示的な宣言がある場合
+            InstanceBox::from_declaration(
+                name.to_string(),
+                decl.fields.clone(),
+                decl.methods.clone(),
+            )
+        } else {
+            // MIR関数から検出された場合 (宣言なし)
+            // 最小限のInstanceBoxを作成 (メソッドはMIR関数テーブルにある)
+            InstanceBox::from_declaration(name.to_string(), vec![], HashMap::new())
+        };
+
+        if std::env::var("NYASH_STATIC_BOX_REGISTRY_TRACE")
+            .ok()
+            .as_deref()
+            == Some("1")
+        {
+            eprintln!(
+                "[static-box-registry] created singleton instance for '{}'",
+                name
+            );
+        }
+
+        self.instances.insert(name.to_string(), instance);
+        Ok(self.instances.get_mut(name).unwrap())
+    }
+
+    /// シングルトンインスタンスが既に作成済みか確認
+    #[allow(dead_code)]
+    pub fn has_instance(&self, name: &str) -> bool {
+        self.instances.contains_key(name)
+    }
+
+    /// 登録済み/検出済みの静的Box名一覧
+    pub fn all_box_names(&self) -> impl Iterator<Item = &String> {
+        self.declarations
+            .keys()
+            .chain(self.detected_boxes.iter())
+    }
+
+    /// declarations への直接アクセス (既存コードとの互換性)
+    pub fn declarations(&self) -> &HashMap<String, BoxDeclaration> {
+        &self.declarations
+    }
+
+    /// detected_boxes への直接アクセス
+    #[allow(dead_code)]
+    pub fn detected_boxes(&self) -> &HashSet<String> {
+        &self.detected_boxes
+    }
+}
+
+impl Default for StaticBoxRegistry {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_static_method_name() {
+        assert_eq!(
+            naming::parse_static_method_name("JsonParserBox.parse/1"),
+            Some(("JsonParserBox".to_string(), "parse".to_string(), 1))
+        );
+        assert_eq!(
+            naming::parse_static_method_name("MyBox.toString/0"),
+            Some(("MyBox".to_string(), "toString".to_string(), 0))
+        );
+        assert_eq!(naming::parse_static_method_name("main"), None);
+        assert_eq!(naming::parse_static_method_name("no_dot"), None);
+    }
+
+    #[test]
+    fn test_static_method_name() {
+        assert_eq!(
+            naming::static_method_name("JsonParserBox", "parse", 1),
+            "JsonParserBox.parse/1"
+        );
+    }
+
+    #[test]
+    fn test_detect_from_mir_functions() {
+        let mut registry = StaticBoxRegistry::new();
+        let fn_names = vec![
+            "JsonParserBox.parse/1".to_string(),
+            "JsonParserBox.toString/0".to_string(),
+            "ProgramJSONBox.get/1".to_string(),
+            "Main.main/0".to_string(), // 除外される
+            "StringBox.length/0".to_string(), // 除外される
+        ];
+
+        registry.detect_from_mir_functions(fn_names.iter());
+
+        assert!(registry.exists("JsonParserBox"));
+        assert!(registry.exists("ProgramJSONBox"));
+        assert!(!registry.exists("Main")); // 除外
+        assert!(!registry.exists("StringBox")); // 除外
+    }
+
+    #[test]
+    fn test_get_or_create_instance() {
+        let mut registry = StaticBoxRegistry::new();
+        registry.detected_boxes.insert("TestBox".to_string());
+
+        let result = registry.get_or_create_instance("TestBox");
+        assert!(result.is_ok());
+
+        // 2回目も同じインスタンスを返す
+        assert!(registry.has_instance("TestBox"));
+    }
+
+    #[test]
+    fn test_nonexistent_box_error() {
+        let mut registry = StaticBoxRegistry::new();
+        let result = registry.get_or_create_instance("NonExistent");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("not found in registry"));
+    }
+}
diff --git a/src/runner/modes/vm.rs b/src/runner/modes/vm.rs
index f1a7724d..016f5e34 100644
--- a/src/runner/modes/vm.rs
+++ b/src/runner/modes/vm.rs
@@ -496,74 +496,11 @@ impl NyashRunner {
         use crate::backend::MirInterpreter;
         let mut vm = MirInterpreter::new();
 
-        // Register static box declarations for singleton persistence
+        // Register static box declarations for singleton persistence (AST-based)
         for (name, decl) in static_box_decls {
             vm.register_static_box_decl(name, decl);
         }
 
-        // 🎯 Phase 173-B: Register using-imported static boxes from MIR function names
-        // Extract box names from MIR function patterns like "BoxName.method/arity"
-        // This enables VM singleton creation for using-imported static boxes
-        {
-            use std::collections::HashSet;
-            let mut imported_boxes: HashSet<String> = HashSet::new();
-
-            for fn_name in module_vm.functions.keys() {
-                // Parse "BoxName.method/arity" pattern
-                if let Some(dot_pos) = fn_name.find('.') {
-                    let box_name = &fn_name[..dot_pos];
-                    // Skip known non-static boxes (runtime data boxes)
-                    if !matches!(
-                        box_name,
-                        "Main"
-                            | "main"
-                            | "StringBox"
-                            | "IntegerBox"
-                            | "BoolBox"
-                            | "ArrayBox"
-                            | "MapBox"
-                            | "FileBox"
-                            | "NetBox"
-                    ) {
-                        imported_boxes.insert(box_name.to_string());
-                    }
-                }
-            }
-
-            // Register any boxes not already in static_box_decls
-            for box_name in imported_boxes {
-                if !vm.has_static_box_decl(&box_name) {
-                    // Create minimal BoxDeclaration for using-imported boxes
-                    // VM only needs the name for singleton creation
-                    let decl = crate::core::model::BoxDeclaration {
-                        name: box_name.clone(),
-                        fields: Vec::new(),
-                        public_fields: Vec::new(),
-                        private_fields: Vec::new(),
-                        methods: std::collections::HashMap::new(),
-                        constructors: std::collections::HashMap::new(),
-                        init_fields: Vec::new(),
-                        weak_fields: Vec::new(),
-                        is_interface: false,
-                        extends: Vec::new(),
-                        implements: Vec::new(),
-                        type_parameters: Vec::new(),
-                    };
-                    if std::env::var("NYASH_USING_STATIC_BOX_TRACE")
-                        .ok()
-                        .as_deref()
-                        == Some("1")
-                    {
-                        eprintln!(
-                            "[phase173-b] Registering using-imported static box: {}",
-                            box_name
-                        );
-                    }
-                    vm.register_static_box_decl(box_name, decl);
-                }
-            }
-        }
-
         // Optional: verify MIR before execution (dev-only)
         if crate::config::env::env_bool("NYASH_VM_VERIFY_MIR") {
             let ring0 = crate::runtime::ring0::get_global_ring0();