diff --git a/src/mir/builder/control_flow/joinir/patterns/pattern_pipeline.rs b/src/mir/builder/control_flow/joinir/patterns/pattern_pipeline.rs
index a65ba60d..ea3004cb 100644
--- a/src/mir/builder/control_flow/joinir/patterns/pattern_pipeline.rs
+++ b/src/mir/builder/control_flow/joinir/patterns/pattern_pipeline.rs
@@ -178,19 +178,27 @@ impl PatternPipelineContext {
     ///
     /// Returns true if:
     /// 1. loop_body contains an if statement
-    /// 2. carrier composition matches if-sum pattern (1 counter + 1-2 accumulators)
+    /// 2. if condition is a simple comparison (var CmpOp literal) - Phase 219-fix
+    /// 3. carrier composition matches if-sum pattern (1 counter + 1-2 accumulators)
     ///
     /// This determines whether to use AST-based lowering or legacy PoC lowering.
     pub fn is_if_sum_pattern(&self) -> bool {
         // Check if loop_body has if statement
-        let has_if = self.loop_body.as_ref().map_or(false, |body| {
-            body.iter().any(|stmt| matches!(stmt, ASTNode::If { .. }))
-        });
-
-        if !has_if {
+        let if_stmt = self.extract_if_statement();
+        if if_stmt.is_none() {
             return false;
         }
 
+        // Phase 219-fix: Check if if condition is a simple comparison
+        // Complex conditions (e.g., i % 2 == 1) → fallback to legacy mode
+        if let Some(ASTNode::If { condition, .. }) = if_stmt {
+            use crate::mir::join_ir::lowering::condition_pattern::is_simple_comparison;
+            if !is_simple_comparison(condition) {
+                // Complex condition → legacy mode (PoC lowering)
+                return false;
+            }
+        }
+
         // Phase 219: Use assignment-based carrier detection
         // (1 counter like "i" + 1-2 accumulators like "sum", "count")
         use crate::mir::join_ir::lowering::loop_update_summary::analyze_loop_updates_from_ast;
diff --git a/src/mir/join_ir/lowering/condition_pattern.rs b/src/mir/join_ir/lowering/condition_pattern.rs
new file mode 100644
index 00000000..84adfa67
--- /dev/null
+++ b/src/mir/join_ir/lowering/condition_pattern.rs
@@ -0,0 +1,255 @@
+//! ConditionPatternBox: if条件パターン判定
+//!
+//! Phase 219 regression fix: if条件が「単純比較」かどうかを判定
+//!
+//! ## 問題
+//!
+//! Phase 219で `is_if_sum_pattern()` をAST-basedに変更した結果、
+//! `loop_if_phi.hako` のような複雑条件 (`i % 2 == 1`) を
+//! if-sumパターンと誤判定してしまう問題が発生。
+//!
+//! ## 解決策
+//!
+//! ConditionPatternBox を導入し、if条件が「単純比較」かどうかを判定する。
+//! AST-based lowerer は単純比較のみ処理可能とし、複雑条件はlegacy modeへフォールバック。
+//!
+//! ## 単純比較の定義
+//!
+//! 以下のパターンのみ if-sum lowerer で処理可能：
+//! - `var > literal` (e.g., `i > 0`)
+//! - `var < literal` (e.g., `i < 10`)
+//! - `var >= literal`
+//! - `var <= literal`
+//! - `var == literal`
+//! - `var != literal`
+//!
+//! ## 複雑条件（legacy mode へフォールバック）
+//!
+//! - `i % 2 == 1` (BinaryOp in LHS)
+//! - `a && b` (複合条件)
+//! - `method_call() > 0` (MethodCall)
+//! - その他
+
+use crate::ast::{ASTNode, BinaryOperator};
+
+/// if条件のパターン種別
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ConditionPattern {
+    /// 単純比較: var CmpOp literal (e.g., i > 0)
+    SimpleComparison,
+    /// 複雑条件: BinaryOp, MethodCall, etc.
+    Complex,
+}
+
+/// if条件ASTを分析してパターンを判定
+///
+/// # Arguments
+///
+/// * `cond` - if条件のASTノード
+///
+/// # Returns
+///
+/// - `ConditionPattern::SimpleComparison` - 単純比較（AST-based lowerer で処理可能）
+/// - `ConditionPattern::Complex` - 複雑条件（legacy mode へフォールバック）
+///
+/// # Examples
+///
+/// ```rust
+/// // Simple: i > 0
+/// let simple = ASTNode::BinaryOp {
+///     operator: BinaryOperator::Greater,
+///     left: Box::new(ASTNode::Variable { name: "i".to_string(), span: Span::unknown() }),
+///     right: Box::new(ASTNode::Literal { value: LiteralValue::Integer(0), span: Span::unknown() }),
+///     span: Span::unknown(),
+/// };
+/// assert_eq!(analyze_condition_pattern(&simple), ConditionPattern::SimpleComparison);
+///
+/// // Complex: i % 2 == 1
+/// let complex = ASTNode::BinaryOp {
+///     operator: BinaryOperator::Equal,
+///     left: Box::new(ASTNode::BinaryOp { ... }), // BinaryOp in LHS
+///     right: Box::new(ASTNode::Literal { value: LiteralValue::Integer(1), span: Span::unknown() }),
+///     span: Span::unknown(),
+/// };
+/// assert_eq!(analyze_condition_pattern(&complex), ConditionPattern::Complex);
+/// ```
+pub fn analyze_condition_pattern(cond: &ASTNode) -> ConditionPattern {
+    match cond {
+        // Comparison operators: ==, !=, <, >, <=, >=
+        ASTNode::BinaryOp { operator, left, right, .. } => {
+            // Check if operator is a comparison
+            let is_comparison = matches!(
+                operator,
+                BinaryOperator::Equal
+                    | BinaryOperator::NotEqual
+                    | BinaryOperator::Less
+                    | BinaryOperator::Greater
+                    | BinaryOperator::LessEqual
+                    | BinaryOperator::GreaterEqual
+            );
+
+            if !is_comparison {
+                // Not a comparison (e.g., And, Or) → Complex
+                return ConditionPattern::Complex;
+            }
+
+            // Check if LHS is a simple variable
+            let left_is_var = matches!(left.as_ref(), ASTNode::Variable { .. });
+
+            // Check if RHS is a literal
+            let right_is_literal = matches!(right.as_ref(), ASTNode::Literal { .. });
+
+            if left_is_var && right_is_literal {
+                ConditionPattern::SimpleComparison
+            } else {
+                // Complex LHS/RHS (e.g., i % 2 == 1, method_call() > 0)
+                ConditionPattern::Complex
+            }
+        }
+        // Any other node type → Complex
+        _ => ConditionPattern::Complex,
+    }
+}
+
+/// if条件が単純比較かどうか
+///
+/// # Arguments
+///
+/// * `cond` - if条件のASTノード
+///
+/// # Returns
+///
+/// `true` if 単純比較（AST-based lowerer で処理可能）
+///
+/// # Examples
+///
+/// ```rust
+/// // i > 0 → true
+/// assert!(is_simple_comparison(&simple_condition));
+///
+/// // i % 2 == 1 → false
+/// assert!(!is_simple_comparison(&complex_condition));
+/// ```
+pub fn is_simple_comparison(cond: &ASTNode) -> bool {
+    analyze_condition_pattern(cond) == ConditionPattern::SimpleComparison
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::ast::{LiteralValue, Span};
+
+    // Helper: Create a simple variable node
+    fn var(name: &str) -> ASTNode {
+        ASTNode::Variable {
+            name: name.to_string(),
+            span: Span::unknown(),
+        }
+    }
+
+    // Helper: Create an integer literal node
+    fn int_lit(value: i64) -> ASTNode {
+        ASTNode::Literal {
+            value: LiteralValue::Integer(value),
+            span: Span::unknown(),
+        }
+    }
+
+    // Helper: Create a BinaryOp node
+    fn binop(op: BinaryOperator, left: ASTNode, right: ASTNode) -> ASTNode {
+        ASTNode::BinaryOp {
+            operator: op,
+            left: Box::new(left),
+            right: Box::new(right),
+            span: Span::unknown(),
+        }
+    }
+
+    #[test]
+    fn test_simple_comparison_greater() {
+        // i > 0
+        let cond = binop(BinaryOperator::Greater, var("i"), int_lit(0));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::SimpleComparison);
+        assert!(is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_simple_comparison_less() {
+        // i < 10
+        let cond = binop(BinaryOperator::Less, var("i"), int_lit(10));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::SimpleComparison);
+        assert!(is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_simple_comparison_equal() {
+        // i == 5
+        let cond = binop(BinaryOperator::Equal, var("i"), int_lit(5));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::SimpleComparison);
+        assert!(is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_simple_comparison_not_equal() {
+        // i != 0
+        let cond = binop(BinaryOperator::NotEqual, var("i"), int_lit(0));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::SimpleComparison);
+        assert!(is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_complex_binop_in_lhs() {
+        // i % 2 == 1 (BinaryOp in LHS)
+        let lhs = binop(BinaryOperator::Modulo, var("i"), int_lit(2));
+        let cond = binop(BinaryOperator::Equal, lhs, int_lit(1));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::Complex);
+        assert!(!is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_complex_binop_in_rhs() {
+        // i == a + b (BinaryOp in RHS)
+        let rhs = binop(BinaryOperator::Add, var("a"), var("b"));
+        let cond = binop(BinaryOperator::Equal, var("i"), rhs);
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::Complex);
+        assert!(!is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_complex_logical_and() {
+        // a && b (logical And)
+        let cond = binop(BinaryOperator::And, var("a"), var("b"));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::Complex);
+        assert!(!is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_complex_logical_or() {
+        // a || b (logical Or)
+        let cond = binop(BinaryOperator::Or, var("a"), var("b"));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::Complex);
+        assert!(!is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_complex_method_call() {
+        // method_call() > 0 (MethodCall in LHS)
+        let method_call = ASTNode::MethodCall {
+            object: Box::new(var("obj")),
+            method: "get".to_string(),
+            arguments: vec![],
+            span: Span::unknown(),
+        };
+        let cond = binop(BinaryOperator::Greater, method_call, int_lit(0));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::Complex);
+        assert!(!is_simple_comparison(&cond));
+    }
+
+    #[test]
+    fn test_complex_non_binary_op() {
+        // Just a variable (not a comparison)
+        let cond = var("condition");
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::Complex);
+        assert!(!is_simple_comparison(&cond));
+    }
+}
diff --git a/src/mir/join_ir/lowering/mod.rs b/src/mir/join_ir/lowering/mod.rs
index 78552903..c169c446 100644
--- a/src/mir/join_ir/lowering/mod.rs
+++ b/src/mir/join_ir/lowering/mod.rs
@@ -25,6 +25,7 @@ pub(crate) mod carrier_update_emitter; // Phase 179: Carrier update instruction
 pub(crate) mod common; // Internal lowering utilities
 pub mod complex_addend_normalizer; // Phase 192: Complex addend normalization (AST preprocessing)
 pub mod condition_env; // Phase 171-fix: Condition expression environment
+pub mod condition_pattern; // Phase 219-fix: If condition pattern detection (simple vs complex)
 pub mod loop_body_local_env; // Phase 184: Body-local variable environment
 pub mod loop_body_local_init; // Phase 186: Body-local init expression lowering
 pub(crate) mod condition_lowerer; // Phase 171-fix: Core condition lowering logic