To correct distortions generated in an amplifier.

A signal amplifier is provided with a delta-sigma modulating means, pulse width modulating (PWM) means, amplifying means, rise detection means, fall detection means, calculating means and adding means. The PWM means applies PWM to a signal S1, outputted from the delta-sigma modulating means. The amplifying means amplifies a signal S2, which is subjected to the PWM into a signal S3 having a prescribed size. The rise detection means compares the signal S2 with the signal S3, to detect the difference in rise between the signals S2 and S3. The fall detection means compares the signal S2 with the signal S3, to detect the difference in fall between the signals S2 and S3. The calculating means calculates the distortion amount generated, depending on characteristics of a circuit connected a stage following to the amplifying means, on the basis of the differential in rise detected by the rise detection means and the differential in fall detected by the fall detection means. The adding means adds the distortion amount calculated by the calculating means to the output of a quantizer of the delta-sigma modulating means.