To generate a PWM signal more closely approximating a PWM signal with respect to a polarity inverted signal of an analog signal by interpolating a polarity inverted signal of an input digital signal to generate a second PWM signal, to obtain tri-state value PWM modulation for attaining reduction in even-order nonlinear distortion and the enhancement of power efficiency and to reduce quantization noise at an audible band when an input signal is a digital signal.

A digital signal converter 2 includes: an over-sampling circuit 21 for sampling a received digital signal by using a high frequency; a polarity inverting circuit 22 for inverting the polarity of the sampled digital signal; interpolation circuits (A)23 and (B)24 for interpolating the respective digital signals; noise shaping circuits (A)25 and (B)26 for shaping the noise of the interpolated signals; PWM conversion circuits (A)27 and (B)28 for applying PWM conversion to a signal whose noise is shaped; and a switching circuit 29 for driving a load on the basis of the PWM signals from the PWM conversion circuits (A)27 and (B)28.