PURPOSE: To prevent the generation of characteristic deterioration and malfunction by reducing carrier leakage from a feedback loop to an input in a pulse width modulating amplifier having the feedback loop from an output to an input.

CONSTITUTION: A buffer 1 is connected to a comparator 3, a carrier signal from an oscillator 2 is also connected to the comparator 3, the comparator 3 is connected to a power switch part 4, the switch part 4 is connected to a demodulating filter 5, and the filter 5 is connected to a load 6. Since negative feedback from a point (b) to a point (a) through a low pass filter (LPF) 7 is performed and a suppression signal part 8 is connected.in parallel with the LPF 7, carrier leakage can be reduced and the generation of characteristic deterioration and malfunction can be prevented.