To provide a feedforward amplifier that detects distortion in a distortion detection loop without the use of a pilot signal, stably detects distortion and amplifies an input signal, even when the input level fluctuates greatly.

A hybrid 1 in the distortion detection loop of the feedforward amplifier distributes an input signal into two. A vector modulator 2 adjusts the phase and amplitude of one of the distributed signals and a main amplifier 3 amplifies this signal. A directional coupler 24 combines the signal having distortion by the main amplifier 3 with the other distributed signal in an opposite phase at the hybrid 1. The input signal is suppressed by this combining. A distortion detection loop control circuit 18 controls the modulator 2, so that the difference between the voltage level of the input signal and the voltage level of the suppressed input signal is maximized.