PURPOSE: To reduce the power consumption of the device.

CONSTITUTION: The collector of a transistor TR T2 for signal amplification is connected to a power source VCC without passing a TR T1 as a switch, and resistances R1 and R2 which give a bias to the TR T2 are connected to the power source V through the TR T1. Thus, a voltage VCE between the collector and the emitter of the TR T2 is not affected by a voltage drop VDROP in the TR T1 and is equal to the supply voltage VCC when the TR T1 is turned on to start the supply of power VCC to resistances R1 and R2.