A three-phase synchronous electric motor, especially a motor of a motorized fan unit for a motor vehicle, includes a synchronizing device in which the energizing signal for the three phases of the motor is synchronized with the rotational position of the rotor. The energizing signals are synchronized with a single position signal representing the rotational position of the rotor, and, in order to start the motor, its three phases are supplied with three energizing signals out of phase one with another by 2.pi./3; if the motor then fails to start, the energizing signals are phase shifted by 2.pi./3.