An expansion unit 50, 60 or 70 is connected to a controller body 10 including an analog direction key 12, a digital direction key 14, command buttons 20a-20z, command levers 22l, 22r, etc. An expansion unit 50 including a photo emitting unit 52 is connected to thereby make the controller cordless. An expansion unit 60 including a photo detecting unit 65, whereby shooting games in which an enemy on a monitor screen can be shot can be played. An expansion unit 70 including a vibration unit 75 is connected, whereby a vibration is given to the controller body 10 to make a shooting game more realistic. New functions can be added to the conventional controller, and the new functions can be added freely without making no change to the controller body.