To reduce an adjacent channel leakage electric power resulting from frequency band widening in a predistorter of an amplifier used for a mobile communication etc.

The differential and integration of an input signal are carried out, and a correction factor is generated to the integration result, in a predistorter of the amplifier which multiplies an input signal, respectively and which makes into a distortion signal, with a signal deformed by a reverse characteristic of the input to output characteristics of the amplifier for the input signal input into the amplifier, in order to reduce the adjacent channel leakage electric power of an amplifier output. It is constituted so that it might consider as a final predistortion signal by multiplying the input signal also by a correction factor.