diff --git a/common_const.py b/common_const.py
new file mode 100644
index 0000000..7f32eb1
--- /dev/null
+++ b/common_const.py
@@ -0,0 +1,7 @@
+from pydantic import BaseModel
+
+
+class Window (BaseModel, frozen = True):
+    WIDTH: int = 1024
+    HEIGHT: int = 768
+
diff --git a/main.py b/main.py
index 389489f..1a4b54e 100644
--- a/main.py
+++ b/main.py
@@ -12,6 +12,7 @@ from playsound import playsound
 from pygame.locals import *
 
 from aques import Aques
+from common_const import *
 from common_module import CommonModule
 from mode import Mode
 from talk import Talk
@@ -35,9 +36,9 @@ class Main:
         print (mode)
 
         pygame.init ()
-        screen: pygame.Surface = pygame.display.set_mode ((1024, 768))
+        screen: pygame.Surface = pygame.display.set_mode ((Window.WIDTH, Window.HEIGHT))
         balloon = pygame.transform.scale (pygame.image.load ('talking.png'),
-                                          (1024, 384))
+                                          (Window.WIDTH, 384))
         if goatoh_mode:
             balloon = pygame.transform.flip (balloon, False, True)
         pygame.mixer.init (frequency = 44100)