PURPOSE: To provide an excellent PWM circuit having a small size and a high efficiency by reducing a cost and current consumption by decreasing the number of elements.

CONSTITUTION: The PWM modulator comprises comparing means 5 for inputting a signal to be modulated to a positive input terminal, a modulation signal to a negative input terminal, producing 3-state type inverted, noninverted outputs and having an output control terminal for controlling the outputs, and pulse generating means 7 connected to output control terminals O, E of the means 5 to output a gate signal synchronized with the modulation signal in the same frequency as that of the modulation signal to the terminals O, E. The inverted output of the means 5 is pulled up to a positive power source through a resistor and the noninverted output of the means 5 is pulled down to a ground through a resistor, and the means 5 thus simultaneously outputs the noninverted signal limited in a maximum duty by the duty value of the gate signal and the inverted signal having a reverse phase to that of the noninverted output signal.