Abstract: In an RF power amplifier, an input-side RF terminal is connected to a gate of an FET via an input-side matching line. A source of the FET is grounded. A drain of the FET is connected to an output-side RF terminal via an output-side matching line. To a line connected to the drain of the FET, a circuit for controlling an output impedance for the secondary harmonic wave is connected, including a first line and a first capacitor. To a line connected to the gate of the FET, a circuit for controlling an input impedance for the secondary harmonic wave is connected, including a second line and a second capacitor. The length of the second line is set so that an electric length thereof becomes longer than one-fourth of the wavelength for the fundamental wave frequency. Thus, an impedance for the harmonic wave is controlled at the input side of the power transistor.