A motor can be driven so that the total loss of a loss of a motor and a loss of an inverter decreases. In a relationship between an optimum carrier frequency at which the total loss is minimized and a torque of a motor M, a lowest value of the optimum carrier frequency is derived, and a relationship between the torque of the motor M and the carrier frequency is determined to have a portion in which the carrier frequency is substantially constant or decreases as the torque of the motor M increases in a range equal to or less than the torque of the motor M corresponding to the lowest optimum carrier frequency and a portion in which the carrier frequency is substantially constant or increases as the torque of the motor M increases in a range equal to or more than the torque of the motor M corresponding to the lowest optimum carrier frequency.