The present invention provides a PWM power amplifier and a method for controlling the same which can improve the sound quality significantly in real time. There is provided a PWM power amplifier and a method for controlling the same that PWM-power-amplifies an input audio signal to supply thus amplified audio signal to a speaker, which power-amplifies the audio signal, removes high frequency signal components included in the audio signal which is power-amplified, detects a distortion error raised in the audio signal which has its high frequency signal components removed based on the audio signal just about to be power-amplified, adjusts a voltage supplied from an external power source depending on a detected distortion error, and adjusts a voltage to be supplied at the time of the power amplification by a value corresponding to the distortion error so as to reduce the output impedance of the audio signal which has its high frequency signal components removed.