PURPOSE: To improve the recovery efficiency of regenerated power and to improve traveling properties at the time of power driving.

CONSTITUTION: A rotary electric machine controller 12 is connected to both terminals of a serial power supply circuit having a large-capacity capacitor 11 and a DC power supply 10 through a reversible chopper. The chopper is connected to one electrode of the controller 12 in which a first switching element 13 is connected at its one terminal to one electrode of the power source 10 so as to be forward in a conducting direction. A second switching element 16 is connected in parallel between the electrodes of the controller 12, a third switching element 17 is connected between the power source 10 and the capacitor 11 and between the element 13 and the element 16 so as to be reverse to the conducting direction of the element 13, and diodes 18-20 are connected in anti-parallel with the respective elements.