In a mobile type X-ray apparatus, an input shaft of a cyclo-decelerator is connected to one end of a rotational shaft of a motor, and the other end of the rotational shaft is connected to an encoder and an electromagnetic brake. The cyclo-decelerator is attached to a frame. Also, a bearing is fitted in the frame, and a wheel hub is fitted between the bearing and a motor output shaft. A wheel is fixed to the wheel hub. By the cyclo-decelerating mechanism, a transmission of power is carried out among contact surfaces of an eccentric cam, epitrochoid teeth and rollers, so that the apparatus has a compact structure with a low noise and no backlash.