PURPOSE: To avoid time delay by turning on a transistor (TR) switch circuit by the potential difference between a power supply voltage and an output of an integration circuit and turning on a muting TR with the output at the on/off of the power supply voltage.

CONSTITUTION: The integration circuit comprising a resistor 4, a diode 5, and a capacitor 6 is provided between a power supply input terminal 1 and ground and a base is onnected to a connecting point between the resistor 4 and the diode 5 via a resistor 7. The device is formed by the TR8 whose emitter is connected to the power input terminal and the TR9 whose emitter is connected between the diode 5 and the capacitor 6 of the integration circuit, whose collector is connected to the collector of the TR8. Then, the muting is applied without time delay and the time constant at the power supply on/off is decided by one integration circuit.