A conventional power amplifying device has a problem that when a signal band is widened, sampling frequency for distortion detection is increased and an FFT calculation amount of a distortion compensation unit is increased, which increase a circuit size and power consumption. The present invention provides a non-linear distortion detection method and a distortion compensation amplifying device capable of suppressing increase of the circuit size and the power consumption even if the signal band is widened. A signal obtained by feeding back an output of a power amplifier is sampled by an A/D converter. An equalizer of a distortion detection unit uses an input signal d(n) of a predistorter as a reference symbol to detect an equalization error e(n) of the orthogonal demodulation signal u(n). An absolute value averaging unit outputs an absolute value of the equalization error e(n) which has been temporally averaged to E(n) as a distortion value to a control unit. According to the distortion value, the control unit adaptively controls the predistorter to perform distortion compensation.