There is provided an inverter capable of reducing a speed in a short period of time without generating an overcurrent even in a case of an alternating current motor which is easy to be saturated magnetically.A frequency of driving a motor is calculated by using a detecting value constituted by passing a direct current bus line voltage through a first filter portion, a voltage command is corrected by using a detecting value passing through a second filter portion, by making a time constant of the second filter portion larger than a time constant of the first filter portion in reducing a speed, the motor is brought into an overexcited state and loss is brought about in the motor.