PURPOSE: To amplify even a rapid input faithfully, by providing a means which holds the crest value of the output of a PWM amplifier which supplies power to an amplifier and comparing output voltages of the amplifier and the PWM amplifier with each other and switching the power source for the amplifier to the holding means by this comparison output.

CONSTITUTION: The input from an input terminal 11 is not only inputted to an amplifier 12 but also inputted to PWM amplifiers 15 and 16 through envelope detecting and level shifting circuits 13 and 14, and the amplifier 12 uses outputs of these PWM amplifiers as power. Outputs of PWM amplifiers are outputted to a peak holding circuit consisting of a resistance, a diode, and a capacitor. If the input becomes rapid, outputs of PWM amplifiers cannot respond, and outputs become a voltage lower than a required voltage. It is detected by comparators 21 and 22, and transistors 32 and 33 are made conductive, and a peak voltage charged in capacitors 27 and 28 is supplied to the amplifier.