PURPOSE: To make the generator highly efficient by varying a hysteresis voltage width of a voltage comparator means in response to the input voltage at a 2nd power terminal connected to the voltage comparison means.

CONSTITUTION: The terminal voltage of a capacitor 1 is monitored by a voltage comparator means 6 having a hysteresis and the hysteresis voltage of the voltage comparator means 6 is varied with a voltage at the 2nd power terminal 13. Thus, a triangle wave signal with nearly equal hysteresis voltage is outputted. Thus, the power voltage of output stage of a PWM(pulse width modulation) amplifier is applied to the 2nd power terminal 13, the PWM modulator capable of compensating the power fluctuation of the output stage effectively is constituted.