Ventilation apertures are respectively formed circumferentially so as to pass axially through an inner circumferential side of a rotor core, rotor grooves are respectively formed circumferentially on an outer circumferential surface of the rotor core so as to have groove directions in an axial direction, and a centrifugal fan is fixed to the shaft at an end of the rotor core near the front frame, and a cyclic path is formed in which, during operation of the centrifugal fan, cooling air flows into the ventilation apertures from near a rear frame, passes through the ventilation apertures and flows out near the front frame, flows radially outward near the front frame and flows into the rotor grooves, passes through the rotor grooves and flows out near the rear frame, and flows radially inward near the rear frame and flows into the ventilation apertures.