diff --git a/poketch/draw.h b/poketch/draw.h
index 429fbaa..9f27221 100644
--- a/poketch/draw.h
+++ b/poketch/draw.h
@@ -20,7 +20,7 @@ class Draw
     const int16_t _pen_out = 12;
 
     const int16_t dot = 4;
-    const int16_t e_rato = 3;
+    const int16_t e_ratio = 3;
 
     LGFX_Sprite sprite_pen;
     LGFX_Sprite sprite_eraser;
@@ -273,10 +273,12 @@ void Draw::drawDot(int16_t x, int16_t y)
         else
         {
             // 消しゴム
-            lcd.fillRect(floor(x / (dot * e_rato)) * dot * e_rato, floor(y / (dot * e_rato)) * dot * e_rato, dot * e_rato, dot * e_rato, POK_WHITE);
+            int16_t x_eraser = floor(x / (dot * e_ratio)) * dot * e_ratio;
+            int16_t y_eraser = floor(y / (dot * e_ratio)) * dot * e_ratio;
+            lcd.fillRect(x_eraser, y_eraser, std::min(dot * e_ratio, WINDOW_WIDTH - TAB_WIDTH - x_eraser), dot * e_ratio, POK_WHITE);
         }
     }
     Serial.println("drawDot");
 }
 
-#endif // _DG_DRAW_
\ No newline at end of file
+#endif // _DG_DRAW_