PURPOSE: To confirm and refer to a window, which is covered with the other window and not displayed on a screen, by means of a simple operation by specifying a single window according to the number of times of input commands.

CONSTITUTION: When a function key 105 on a keyboard 104 is pushed, the overlapped part of three windows 102, 103 and 109 is displayed on a half-tone basis, and the position and size of the window 109, which has been covered by the window 102 and could not be observed, are confirmed. Next, when a cursor 110 is moved to the position, where the window 109 is displayed on the half-tone basis, by a mouse 106 and a button 108 of the mouse 106 is continuously pushed for two times, the window 109 at the second higher display priority out of the windows 102 and 109 existing at the cursor 110 position is displayed at the highest-order position. Thus, the contents of the window hidden by the other window can be easily referred to.