The apparatus includes: distortion amount detector which detects the amount of distortion of an output signal of an amplifier; parameter holder which holds a parameter having been set therein, the parameter holder being capable of varying the difference according to the parameter set therein; parameter corrector which corrects the parameter held in the parameter holder in such a manner that the distortion amount detected by the distortion amount detector is improved; noise component detector which detects a noise component that can be caused in the output signal resulting from a quadrature modulation; and noise component remover which performs processing for removing the noise component detected by the noise component detector. This arrangement makes it possible to suppress image frequency component generation in an output signal of the amplifier accompanying quadrature modulation and to optimize parameters in distortion compensation.