PURPOSE: To eliminate remaining sound with simple circuit constitution by controlling sound volume with a smoothed output of a pulse width modulation (PWM) signal for sound volume control and applying muting to sound at the control of minimum sound volume.

CONSTITUTION: A PWM output signal for controlling sound volume of a control circuit 1 is smoothed and impreseed to a sound volume control terminal of a sound amplifier circuit IC8. When the PWM output signal controlling the sound volume to a minimum value is outputted from the control circuit 1, a mute control output signal is generated by extracting a signal from a PWM control circuit in the control circuit 1 or other control so as to apply muting to the sound IC8. Thus, even if a residual voltage is generated to the sound volume control terminal of the sound IC8 at the PWM output signal for the minimum sound volume control, the residual sound is eliminated.