diff --git a/lambda/spilitwise-automation/src/validator/isExpenseEligibleForSplitting.ts b/lambda/spilitwise-automation/src/validator/isExpenseEligibleForSplitting.ts
index bb1f048..31fc7e3 100644
--- a/lambda/spilitwise-automation/src/validator/isExpenseEligibleForSplitting.ts
+++ b/lambda/spilitwise-automation/src/validator/isExpenseEligibleForSplitting.ts
@@ -40,18 +40,28 @@ export const isExpenseEligibleForSplitting = ({
     return false;
   }
 
-  const { cost, users } = expense;
+  const { cost, users, created_at } = expense;
   const splitRate = parseFloat(
     (parseInt(users?.[0]?.owed_share ?? "0") / parseInt(cost)).toPrecision(2)
   );
+  const isCurrentMonth = (created_at: string | undefined) => {
+    if (created_at) {
+      return new Date(created_at).getMonth() === new Date().getMonth();
+    }
+    console.error("created_atが不正です", created_at);
+    return false;
+  };
 
   // グループIDが一致し、割り勘でない、かつ、割り勘率が0,1,USER1_RATE,USER2_RATE以外の場合は処理対象とする
+  // payment:true -> 精算レコード（個々の支払い終了ではない）
+  // 一度いじったものを再度いじらないようにするため、payment以前の対象は除外したいが判定が難しいので今月内のものだけを対象とする
   return (
     expense.payment === false &&
     expense.group_id?.toString() === SPLITWISE_GROUP_ID &&
     splitRate !== 0 &&
     splitRate !== 1 &&
     splitRate !== parseFloat(USER1_RATE) &&
-    splitRate !== parseFloat(USER2_RATE)
+    splitRate !== parseFloat(USER2_RATE) &&
+    isCurrentMonth(created_at)
   );
 };
diff --git a/test/splitExpense.test.ts b/test/splitExpense.test.ts
index b9e4208..48b1319 100644
--- a/test/splitExpense.test.ts
+++ b/test/splitExpense.test.ts
@@ -111,6 +111,16 @@ describe("補正対象判定処理テスト", () => {
       isExpenseEligibleForSplittingWrapper(nonTargetGroupExpense)
     ).toBeFalsy();
   });
+
+  test("前月のデータは対象としない", () => {
+    const nonTargetGroupExpense: components["schemas"]["expense"] = {
+      ...basicExpense,
+      created_at: "2021-08-31T00:00:00Z",
+    };
+    expect(
+      isExpenseEligibleForSplittingWrapper(nonTargetGroupExpense)
+    ).toBeFalsy();
+  });
 });
 
 describe("割り勘補正処理テスト", () => {
@@ -177,6 +187,7 @@ const basicExpense: components["schemas"]["expense"] = {
     },
   ],
   payment: false,
+  created_at: new Date().toISOString(),
 };
 
 const reSplittedExpenseBalance = {