A movement member which reciprocates includes a thick portion and a thin portion, a bearing portion formed in the thick portion is slidingly supported by the guide shaft, and a sliding portion formed in the thin portion is slidingly guided by the sliding guide portion. Power of the motor is transmitted to a pinion gear via a speed reduction gear and a speed reduction mechanism inside a gear box, and a movement reaction force is applied from the pinion gear to the rack portion. Since the rack portion is positioned on an axis Os, a force is effectively applied to the movement member by the power from the motor.