A digital input class-D amplifier includes a decoder which outputs a plurality of lines of time-series digital signals having a density of 1 or 0 conforming to an input digital signal, an error integrator which integrates a difference between a drive waveform to be applied to a load and a sum of the plurality of lines of time-series digital signals output from the decoder, and a modulation circuit which generates a pulse modulated with a pulse width or a pulse density based on a result of integration performed by the error integrator. The load is driven in accordance with the pulse generated by the modulation circuit.