PURPOSE: To enable a stable decelerating operation by decreasing a torque command value when DC supply exceeds a certain voltage.

CONSTITUTION: On power failure, a motor 4 functions as a generator and a capacitor 2 is charged by said generated output. Then, if a voltage between both ends of the capacitor 2 exceeds 300V, a voltage Vk of a value equivalent to an exceeded voltage is outputted from an overvoltage detection circuit 16. If a speed command signal Si is negative, the voltage Vk is outputted from an amplifier control circuit 14 and supplied to a limiter amplifier 15. Accordingly, a positive side limit voltage decrease as much as the voltage Vk to decrease a torque command value TOS outputted from the limiter amplifier 15.