To automatically adjust a feedfoward amplifier optimally by inserting a pilot signal on both sides of an input signal.

A vector adjustment device 12 adjusts the amplitude and the phase of one signal received from an input terminal 15 and distributed by a directional coupler 7, and pilot signals generated by, pilot signal generators 5, 6 are added on both sides of the frequency of the input signal and the result is supplied to a main amplifier 1, where it is amplified. A directional coupler 10 extracts a distortion component that is produced in the amplifier and the pilot signals and they are amplified by an auxiliary amplifier 2 via a vector adjustment device 11. A directional coupler 9 eliminates the distortion component from the output of the auxiliary amplifier 2 and the output of the main amplifier 1 and the result is outputted from an output terminal 16. A control circuit 14 controls the amplitude and the phase of the output signal of the vector adjustment device 11 based on the two pilot signals detected from the output signal to make a cancellation amount of the distortion component constant.