diff --git a/bg-evening.jpg b/bg-evening.jpg
new file mode 100644
index 0000000..d750d53
Binary files /dev/null and b/bg-evening.jpg differ
diff --git a/bg-night.jpg b/bg-night.jpg
new file mode 100644
index 0000000..24c2b52
Binary files /dev/null and b/bg-night.jpg differ
diff --git a/main.py b/main.py
index 772b3c7..b706d4a 100644
--- a/main.py
+++ b/main.py
@@ -1,3 +1,5 @@
+# vim: nosmartindent autoindent
+
 import json
 import random
 import subprocess
@@ -21,7 +23,11 @@ from youtube import *
 
 class Main:
     @classmethod
-    def main (cls, argv: list, argc: int) -> None:
+    def main (
+            cls,
+            argv: list,
+            argc: int) \
+    -> None:
         mode = Mode.NIZIKA
         match (argc > 1) and argv[1]:
             case '-g':
@@ -47,6 +53,16 @@ class Main:
         if goatoh_mode:
             balloon = pygame.transform.flip (balloon, False, True)
 
+        # 背景（夕方）
+        bg_evening: pygame.Surface = pygame.transform.scale (
+            pygame.image.load ('bg-evening.jpg'),
+            (CWindow.WIDTH, CWindow.HEIGHT))
+
+        # 背景（夜）
+        bg_night: pygame.Surface = pygame.transform.scale (
+            pygame.image.load ('bg-night.jpg'),
+            (CWindow.WIDTH, CWindow.HEIGHT))
+
         # 音声再生器の初期化
         pygame.mixer.init (frequency = 44100)
 
@@ -78,7 +94,7 @@ class Main:
         histories: list = []
 
         while (True):
-            screen.fill ((0, 255, 0))
+            cls.draw_bg (screen, bg_evening, bg_night)
 
             # 左上に時刻表示
             for i in range (4):
@@ -201,7 +217,7 @@ class Main:
                         if not double_mode or random.random () < .5:
                             break
 
-                        screen.fill ((0, 255, 0))
+                        cls.draw_bg (screen, bg_evening, bg_night)
 
                         chat_item.author = {'name':     'ゴートうひとり' if goatoh_talking else '伊地知ニジカ',
                                             'id':       '',
@@ -224,8 +240,21 @@ class Main:
                     pygame.quit ()
                     sys.exit ()
 
+    @classmethod
+    def draw_bg (
+            cls,
+            screen:     pygame.Surface,
+            bg_evening: pygame.Surface,
+            bg_night:   pygame.Surface) \
+    -> None:
+        if 17 <= (h := datetime.now ().hour) < 18:
+            screen.blit (bg_evening, (0, 0))
+        elif (h < 6) or (18 <= h):
+            screen.blit (bg_night, (0, 0))
+        else:
+            screen.fill ((0, 255, 0))
+
 
 if __name__ == '__main__':
-    # Main.main ((len (sys.argv) > 1) and (sys.argv[1] == '-g'))
     Main.main (sys.argv, len (sys.argv))