diff --git a/packages/dart_flutter_common/lib/src/date_time.dart b/packages/dart_flutter_common/lib/src/date_time.dart
index e1fa2e63..0b3d3de6 100644
--- a/packages/dart_flutter_common/lib/src/date_time.dart
+++ b/packages/dart_flutter_common/lib/src/date_time.dart
@@ -1,9 +1,67 @@
 import 'package:intl/intl.dart';
 
 extension DateTimeExtension on DateTime {
+
+  /// _daysBeforeメソッドで使用される定数。
+  /// 「N日前」と表示される最小日数を示す。
+  static const _daysBeforeLowerLimit = 2;
+
+  /// _daysBeforeメソッドで使用される定数。
+  /// 「N日前」と表示される最大日数を示す。
+  static const _daysBeforeUpperLimit = 7;
+
   /// 「yyyy年MM月dd日」形式の文字列を返す。
   String formatDate() => DateFormat('yyyy年MM月dd日').format(this);
 
   /// 「yyyy年MM月dd日 HH時mm分」形式の文字列を返す。
   String formatDateTime() => DateFormat('yyyy年MM月dd日 HH時mm分').format(this);
+
+  /// thisと現在時刻と比較して相対的な日付文字列を返す。
+  /// thisが今日であれば、「HH:mm」
+  /// 昨日であれば、「昨日」
+  /// _daysBeforeLowerLimitから_daysBeforeUpperLimitの範囲内であれば、「N日前」
+  /// それ以外は 'yyyy年MM月dd日' 形式の日付
+  String formatRelativeDate() {
+    if (_isToday()) {
+      return DateFormat('HH:mm').format(this);
+    }
+    if (_isYesterday()) {
+      return '昨日';
+    }
+    final daysBeforeResult = _daysBefore();
+    if (daysBeforeResult != null) {
+      return '$daysBeforeResult日前';
+    }
+    return formatDate();
+  }
+
+  /// thisが今日かどうかの真偽値を返す。
+  /// thisと現在時刻の「年、月、日」が全て一致する場合には「今日」であるため真を返す。
+  bool _isToday() {
+    final now = DateTime.now();
+    return year == now.year && month == now.month && day == now.day;
+  }
+
+  /// thisが昨日かどうかの真偽値を返す。
+  /// thisと現在の日付より1日前の「年、月、日」が全て一致する場合には「昨日」であるため真を返す。
+  bool _isYesterday() {
+    final now = DateTime.now();
+    final yesterday = DateTime(now.year, now.month, now.day - 1);
+    return year == yesterday.year &&
+        month == yesterday.month &&
+        day == yesterday.day;
+  }
+
+  /// thisと現在時刻との間の日数を計算し、
+  /// その日数が[_daysBeforeLowerLimit] 日〜 [_daysBeforeUpperLimit] 日の範囲内ならその数字を、
+  /// そうでなければnullを返す
+  int? _daysBefore() {
+    final now = DateTime.now();
+    final difference = now.difference(this).inDays;
+    if (difference >= _daysBeforeLowerLimit &&
+        difference <= _daysBeforeUpperLimit) {
+      return difference;
+    }
+    return null;
+  }
 }
diff --git a/packages/dart_flutter_common/test/date_time_test.dart b/packages/dart_flutter_common/test/date_time_test.dart
index 888069b1..89e8304b 100644
--- a/packages/dart_flutter_common/test/date_time_test.dart
+++ b/packages/dart_flutter_common/test/date_time_test.dart
@@ -1,5 +1,6 @@
 import 'package:dart_flutter_common/dart_flutter_common.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:intl/intl.dart';
 
 void main() {
   group('test DateTimeExtension', () {
@@ -10,11 +11,49 @@ void main() {
       expect('1998年05月02日', formattedDate);
     });
 
-     test('test formatDateTime', () {
+    test('test formatDateTime', () {
       final date = DateTime(1998, 5, 2, 10, 7);
       final formattedDate = date.formatDateTime();
 
       expect('1998年05月02日 10時07分', formattedDate);
     });
+
+    test('test formatRelativeDate for today', () {
+      final now = DateTime.now();
+      final date = DateTime(now.year, now.month, now.day, 12, 15);
+      final formattedRelativeDate = date.formatRelativeDate();
+
+      expect(formattedRelativeDate, DateFormat('HH:mm').format(date));
+    });
+
+    test('test formatRelativeDate for yesterday', () {
+      final now = DateTime.now();
+      final date = DateTime(
+        now.year,
+        now.month,
+        now.day - 1,
+      );
+      final formattedRelativeDate = date.formatRelativeDate();
+
+      expect(formattedRelativeDate, '昨日');
+    });
+
+    for (var i = 2; i <= 7; i++) {
+      test('test formatRelativeDate for $i daysBefore', () {
+        final now = DateTime.now();
+        final date = DateTime(now.year, now.month, now.day - i);
+        final formattedRelativeDate = date.formatRelativeDate();
+
+        expect(formattedRelativeDate, '$i日前');
+      });
+    }
+
+    test('test formatRelativeDate for over a week ago', () {
+      final now = DateTime.now();
+      final date = DateTime(now.year, now.month, now.day - 8);
+      final formattedRelativeDate = date.formatRelativeDate();
+
+      expect(formattedRelativeDate, DateFormat('yyyy年MM月dd日').format(date));
+    });
   });
 }