A transistor (12) of a high-frequency amplifying unit (2) amplifies an inputted high-frequency signal. A measuring circuit (27) measures the amplitude of the inputted high-frequency signal. A bias control circuit (26) continuously controls the bias applied to the transistor (12) according to the measured value of the amplitude. Thus, a steep gain variation with the variation of the amplitude of the inputted high-frequency signal can be suppressed.
