PURPOSE: To make it possible to reduce the number of semiconductor elements and the like, by reconstituting windings and the elements in at least an auxiliary operation mode in which the control semiconductors of a self-synchronous machine required for the fundamental or main operations of an electric motor and a generator correspond to a charger or a transformer.

CONSTITUTION: In an electric motor mode, for instance, E1-E3 and E2-E4 of stator windings (HC) are offset 180 degrees. Choppers a, b, A, B shunt the stator current into HCE1+E2, E3+E2, E3+E4, E1+E4 or direct the current to form a revolving magnetic field. Diodes(DD) d1, d2 protect the choppers A, B. The current Iro of HCE5 controlled by the chopper C and protected by the DD d5 generates the magnetic field for a rotor. Also in a braking generator mode, the increase of the current Iro is represented by that of the electromotive force of the HCE1+E2, E2+E3, E3+E4, E4+E1. If the voltage exceeds the voltage of a battery Vp, a current Ist is allowed to pass, thereby charging the battery Vp.