PURPOSE: To detect voltage variation in a DC voltage source to prevent the use of voltage correction circuit output correcting an output voltage correction command in the case a DC voltage is raised when regeneration is made.

CONSTITUTION: An output voltage command change-over circuit 10 obtaining an output voltage correction circuit 7 output and an output voltage command selector circuit 9 output is constituted, and such a voltage command change-over means as not through the voltage correction circuit during the deceleration of an AC motor is provided.