A Vs (signal) + Vd (distortion) in a main amplifier output path (5) is combined by a power synthesizer (27) with an output G(W) W Vd from an auxiliary amplifier (26), and an error signal Ve (= Vs + (1 + G(W) W) Vd) is inputted from a directional coupler (33) to a control circuit (39) serving as an adaptive filter. Moreover, The output G(W) W Vd of the auxiliary amplifier (26) is extracted from a directional coupler (24) and is divided by a set value W outputted from the control circuit (39) by a divider (38), and G(W) VD is inputted as a reference signal of the control circuit (39).
