A controller of a portable game machine comprises a steering wheel having a body and a rotary unit; a base for locating a portable game machine; a supporting frame for supporting the seat to the steering wheel; and a steering wheel seat for supporting the rotary unit of the steering wheel to a body. The piezoelectric switch is placed on the base, by mechanic linear power transfer, functions of the portable game machine is controlled by operation the steering wheel. By levers to transfer power, the function keys of the steering wheel are corresponding to function keys of the portable game machine.