Abstract: An electric motor has a rotor and a stator each of which is provided with a polyphase winding. The rotor and stator have the same number of poles but the number of phases in the winding of the rotor differs from that in the winding of the stator. The motor can operate as a stepping motor by deenergizing one of the phases of one winding while simultaneously energizing one of the phases of the other winding, and the motor advances one step whenever one phase of a winding is deenergized and, at the same time, one phase of the other winding is energized. The deenergizing and energizing steps are performed alternately for each winding. The motor can further operate as a synchronous motor by accelerating the motor, discontinuing the deenergizing and energizing steps for one of the windings while maintaining the excitation of such winding and, simultaneously with the discontinuing step, reducing the frequency of the deenergizing and energizing steps for the other winding.