A frequency multiplier is constructed to input an input signal to a transistor through an input matching circuit and to output a multiplied output signal from the transistor through a reflecting type fundamental wave signal band suppressing circuit and an output matching circuit. A transmission line produces a standing wave and is disposed between the output terminal of the transistor and the input terminal of the reflecting type fundamental wave signal band suppressing circuit. Because the voltage acting on the output terminal of the transistor consequently increases, the transistor operates at a point at which the nonlinearity of its input-output characteristic is greater and the output power of the multiplied output signal increases.