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 attenuates a component of a frequency fL(=|fr−ft|).