PURPOSE: To prevent output of click noise surely by providing a capacitor for a power-off detection capacitor and a smoothing capacitor in common to a power supply circuit.

CONSTITUTION: When a power siwtch 8 is turned off, a microcomputer power supply circuit 6 is turned off to stop power supply to a microcomputer. Transistors (TRs) 2, 3 are turned off at the same time, a TR4 is turned on, TRs 5, 6 are turned off, an amplifier power circuit 5 is turned off to stop the power supply. As a result, a smoothing capacitor C3 starts discharging the electric charge charged therein, but since the TR5, 6 are both turned off, the discharge current flows to a mute control circuit 3. Then the control circuit 3 turns on a mute TR2 to keep this state until the discharge current is terminated. Thus, the click noise is prevented from being outputted surely.