A pulse width modulation device which a step form control signal generated by a control signal generating device and a triangular wavecarrier signal generated by a carrier generating device are compared by a digital comparator and the comparison signal is supplied to an edge detection device. Also, a top/bottom signal generated by a top/bottom signal generating device is supplied to the edge detection device. The edge detection device includes an edge detection function that generates an edge detection signal by detecting change of the comparison signal. The edge detection function is inhibited by the edge detection signal; and inhibition is cancelled by the top/bottom signal so that the edge detection signal is output. A PWM signal is output from the pulse generating device in accordance with the comparison signal, edge detection signal, and top/bottom signal.