PURPOSE: To decrease effectively noise due to the switching of power supply of a device, by using a capacitor, a diode and a driving transistor(TR) and utilizing the leading/trailing of the power supply of the device for driving a muting circuit.

CONSTITUTION: A current supplied from the power supply 8 of the device is applied to the emitter of a TR6 via a diode (D)2 for reverse flow prevention. The emitter of the TR6 is grounded with a capacitor 1 and the base is connected to the anode of the D2 via a base resistor 5. Further, the base of the TR6 is grounded with a base potential delaying capacitor 3 and connected to a power supply 8 via a discharge D4 thereof. A muting circuit driving current is applied from the collector of the TR6 to a muting circuit 7. The noise due to the switching of the power supply 8 is reduced much effectively in this way.