A feed foward amplifier including a first amplifier for amplifying a first input signal; an extraction unit for extracting a distortion element added to a second signal output from the first amplifier; a second amplifier for amplifying the distortion element; an adder for inverting the phase of either the second signal or of a third signal output from the amplifier and for adding these signals; and a controller for controlling the supply of power to the second amplifier based on a level of the first terminal. When the controller ascertains that the detected level is equal to or greater than the reference level, the controller unit powers on the second amplifier. When the detected level is lower than the reference level, the controller powers off the second amplifier. Thus, since the power to the second amplifier is switched off when the volume of traffic is low, the consumption of power is reduced.