A feedforward amplifier having a distortion detection loop and a distortion elimination loop is provided that achieves increased accuracy, improved response, and stable operation. A variable attenuator is placed in front of a detector in a loop output stage, and the amount of attenuation in the variable attenuator is set large during a transient response period during the rising of the amplifier, and set small during a steady-state condition. The detection of the transition to the steady-state condition is accomplished, for example, by comparing the detector output with a prescribed threshold value. The width of perturbation is set large during a transient response period, and set small during a steady-state condition.