An alternator has front and rear bearings, supported by front and rear frames, to rotatably support a shaft of a rotor extending along axial direction. A washer is located between the rear frame and the rear bearing to apply pressing force to the rear bearing slightly movable along axial direction. The washer has a ring-shaped base portion concentrically located with the rear bearing, slanting portions extending from the base portion toward outside of radial direction such that two adjacent slanting portions arranged as each pair along circumferential direction are inclined to different sides of axial direction, and flattened portions extending from respective slanting portions toward outside and being parallel to the base portion. Flattened portions shifted to front side are in contact with the rear bearing, and flattened portions shifted to rear side are in contact with the rear frame.