United States A body device 2 has left and right display units disposed adjacent to both eyes of a user. A program cartridge 4 is detachably provided to this body device 2. The game cartridge 4 stores program data and image data for eye width/visibility adjusting picture display. The body device 2 reads the program from the program cartridge 4 and executes it immediately after the power is turned on or at the time when the game is temporarily stopped, and reads and refers to the image data to display eye width/visibility adjusting pictures in the left and right display units. Then, the user operates an eye width adjusting lever 201 and a visibility adjusting lever 202 on the upper surface of the body device 2 while watching the eye width/visibility adjusting pictures displayed in the left and right display systems. The space set between the left and right display units is thus adjusted. The visibility adjustment in the left and right display units is also achieved.