A bias current to be supplied to an amplification circuit 60 is drawn out of a collector of a transistor Q11 of a bias circuit 10. The drawn-out bias current is input to a base of a transistor Q13 via an attenuation filter F2 and is output from an emitter of the transistor Q13 in the state where the voltage thereof is reduced by a level corresponding to Vbe. The attenuation filter F2 is conducted in a DC manner, and attenuates a component of a frequency fH(=2ft-fr) defined by a transmission frequency ft and a receiving frequency fr of a radio frequency signal. The bias current output from the emitter of the transistor Q13 is supplied to the amplification circuit 60 via an attenuation filter F1. The attenuation filter F1 is conducted in a DC manner, and attenuates a component of a frequency fL(=|fr-ft|).
