To eliminate unbalance in the three-phase relation, by properly correcting errors due to variations among elements used in a current detection circuit.

A correction coefficient computing unit 10 utilizes an induced voltage produced in the U phase and the V phase, to compute a correction coefficient for the detection value of V-phase motor current, based on the detection values of U-phase and V-phase motor currents obtained when a dynamic brake resistance circuit switching portion 7 switches the path, from a PWM three-phase inverter 1 to dynamic brake resistors 8a, 8b, 8c. A multiplier 12 corrects the detected value of V-phase motor current, based on the correction coefficient for the detected value of V-phase motor current, and thereby corrects the unbalance between the detection values of U-phase and V-phase motor currents.