A key-operating device includes a shell confining a chamber therein and connected to a video game apparatus with depressible keys, a lever pivotally mounted in the chamber and having protrusions projecting toward the keys, a wheel surrounding and connected to the shell and rotatable relative to the shell, and an actuating member projecting from the wheel and engageable with the lever in such a manner that rotation of the wheel results in engagement between the actuating member and the lever so as to permit fulcrum movement of the lever and pressing of the keys by the protrusions.