A predistorter for correcting distortion caused by a memory effect in amplifying a signal by an amplifier is provided. In the memory PD 2 provided to the predistorter, the level detection means 21 detects the level of the signal, the coefficient output means 22 outputs the coefficient corresponding to the detected level, the delay means 23 delays the output coefficient, the difference detection means 24 detects the difference between the output coefficient and the delayed coefficient, the multiplication means 25 multiplies the detected difference with the signal, and the combination means 26 combines the result of the multiplication and the signal. Thus, the result of the combination is output to the amplifier.