For an interval in which an Op-vector and a b-vector are successively output among intervals of output voltage vectors of each phase within a PWM cycle, the output times of each vector are divided by a positive integer m to find divided times of each vector, and the Op-vector and the b-vector are each alternately output for the divided time, each vector being output m times. For an interval in which an On-vector and an a-vector are successively output, the output times of each vector are divided by a positive integer n to find divided times of each vector, and the On-vector and a-vector are each alternately output for the divided time, each vector being output n times. The adoption of this method enables dispersion of the frequency component of current ripple that arises from PWM pulses (1)-(3).