An inverter for controlling the number of revolutions of an induction motor by changing the frequency of a voltage applied to the motor. A pulse width modulation signal is generated by comparing a triangular wave signal which is a carrier frequency signal of an inaudible frequency with a modulated wave signal that is obtained by amplifying an error between a magnetic flux instruction signal of a frequency proportional to an external frequency instruction produced from a magnetic flux instruction signal generating circuit (5) and an integral signal of a voltage applied to a motor (4) from an integration circuit (6) that integrates the output voltages of an inverter unit (3). The above-mentioned structure makes it possible to decrease the distortion in the waveform of an output voltage even when the carrier frequency is set to an inaudible frequency. Therefore, there is provided an inverter which is capable of driving a motor with low noise.
