At least a rotor fixing portion and a bearing fitting portion are combined to form a hollow rotary shaft. The rotor of a rotary motor portion is fixed on the rotor fixing portion. A thrust radial bearing is fitted on the outer periphery of the bearing fitting portion and a screw nut is fitted to the bearing fitting portion. The rotor fixing portion and the bearing fitting portion are coupled with screw member(s) which are inserted into the hollow rotary shaft from one axial end of the hollow rotary shaft and axially extend inside the bearing fitting portion and the rotor fixing portion. A flange portion of the screw nut is fixed on an abutment portion of the bearing fitting portion in abutment with an end surface of an inner race of the thrust radial bearing that is located on the one axial end side.
