A class D amplifier defines different sets of resampled points A and B for channels chA and chB of an input digital audio signal, extracts an interpolation signal of the digital audio signal at the resampled points A and another interpolation signal of the digital audio signal at the resampled points B, and makes a correction to the phase of at least one of the interpolation signals. Thereby, radiation noise can be reduced even if the number of channels of the digital audio signal increases.