PURPOSE: To reduce power consumption and to miniaturize a power amplifier by performing the high-efficiency power amplification of a wave to be modulated.

CONSTITUTION: Carrier-level transistor TRQ1 and modulated-wavelevel TRQ2 are both biased for class "C" amplifying operation, and TRQ2 is biased reversely less than TRQ1. A modulated-wave input from input terminal 40, while supplied to the base of TRQ1 via impedance matching circuit 50 and 90° phase-shifting circuit 60, supplied to the base of TRQ2 via impedance matching circuit 70. Between collectors of TRs Q1 and Q2, impedance inverting circuit 30 is connected and from circuit 30, an output is led out to output terminal 30 via output-side impedance matching circuit 80. Impedance inverting circuit 30 is terminated by load resistances of TRs Q1 and Q2 respectively and operates so that the product those resistances will have a constant value invariably.