PURPOSE: To shoot bullets successively as far as possible by providing a motor switching mechanism interlocked with a trigger, actuating a controller by a signal from a changeover switch provided on a selector of the motor switching mechanism and a signal from the trigger, and driving a piston by an instruction from the controller.

CONSTITUTION: A motor switching mechanism 16 comprises a selector 17, a controller 18, a battery 19, and a switch 20. The selector 17 includes a changeover switch 22 for freely selecting one of three shooting methods: SAFE for holding a state where no bullet 5 is shot when the trigger 21 is operated, SEM 1 for shooting only one bullet 5 with single trigger 21 operation, and AUTO for successively shooting bullets 5 as long as the trigger 21 is pulled out without interruption. One of the shooting methods is instructed to the controller 18 by the operation of the changeover switch 22.