diff --git a/lambda/encise-data-unreceive-check/encise-data-unreceive-check.py b/lambda/encise-data-unreceive-check/encise-data-unreceive-check.py
index d762c275..389c82f9 100644
--- a/lambda/encise-data-unreceive-check/encise-data-unreceive-check.py
+++ b/lambda/encise-data-unreceive-check/encise-data-unreceive-check.py
@@ -223,8 +223,9 @@ def encise_data_unreceive_check(records: list, execute_month: str) -> tuple[list
                         is_file_not_exists = False
                         # 存在したファイルの年月部分を抜き出し、チェック対象年月（処理稼働月-1)である場合
                         match_group_yyyymm = match_result.group(1)
-                        check_target_yyyymm = (datetime.datetime.now(
-                            ZoneInfo(TZ)) - relativedelta(month=1)).strftime('%Y%m')
+                        today = datetime.datetime.now(ZoneInfo(TZ))
+                        minus_1_month = today + relativedelta(months=-1)
+                        check_target_yyyymm = minus_1_month.strftime('%Y%m')
                         if match_group_yyyymm == check_target_yyyymm:
                             logger.info(
                                 f'I-04-04 I/Fファイルの受領を確認しました　ファイル名：{file_name}')