The present invention provides an amplifying apparatus including, two amplifiers for receiving input signals in common and for outputting their respective amplified signals, a combiner for combining the output signals of the two amplifiers and for outputting a combined signal, the amplifying apparatus which inhibit the distortion component in the output of amplifiers in the transition state. This amplifying apparatus comprises, a predistortion unit for determining a distortion compensation component based on the output of the combiner and for predistorting the input based on the determined distortion compensation component, and a gain control unit for attenuating the inputs to set lower than in the steady state by reducing the gain in the transition from two amplifier operation to one amplifier operation, or in the transition from one amplifier operation to two amplifier operation, or at the time of removal or attachment the amplifiers.