PURPOSE: To obtain an AC power amplifier whose output voltage does not include any DC component in the AC power amplifier receiving an AC signal voltage, amplifying its power and supplying power to a load.

CONSTITUTION: A 1st input circuit of a DC bias generating section 3 having two input circuits and one output circuit receives a signal voltage and the output circuit is connected to an input circuit of a gate signal distribution section 5 having one input circuit and two output circuits. Two outputs from the gate signal distribution section 5 are respectively fed to gates of positive and negative field-effect TRs 6, 7 and a combined output voltage of the field-effect transistors 6, 7 is given to a load 8 and an input circuit of a DC bias adjustment section 4. The output of the DC bias adjustment section 4 is given to the 2nd input circuit of the DC bias generating section 3.