In a combination of, for example, a rotor having eight magnetic poles and a stator having twelve slots and pulsating components of permeance, which generate a sinusoidal cogging torque having maxima of the same number as the number of poles of the rotor, pressurizing parts arranged in predetermined positions, applying a force at an outer periphery of the stator and directed inwardly cancels the pulsating components of the cogging torque.