A control method of an inverter for outputting polyphase alternate-current electrical power is provided. In the control method, modified PWM pulses of respective phases for controlling semiconductor switching elements of the inverter are generated, based on an output of a counter common to the respective phases. Each of the modified PWM pulses is configured such that a total pulse width, in a period corresponding to one or more cycles of a carrier, is substantially equal to a total pulse width of an assumed PWM pulse which is obtained by comparing, with the carrier, a time average value of an output voltage of the corresponding phase in the period. Further, at least one of a generation timing and a generation frequency of at least one of the modified PWM pulses is changed from the assumed PWM pulse.