PURPOSE: To keep the DC potential of an output terminal of an amplifier to a half of a power voltage by using a diode and a resistor so as to a current and a voltage, applying the current and the voltage to the object amplifier and relating the resistance value of the resistor to a value of a negative feedback resistor.

CONSTITUTION: A diode D1, a resistor R1 and a transistor (TR) Q7 of diode connection are connected in series between a terminal T1 and ground, and the TR Q7 and a TR Q8 constitute a current mirror circuit 5 using the TR Q7 as the input TR and a common as a reference potential point. Further, collectors of TRs Q3, Q6, are connected to the collector of the TR Q8 and to the inverting input of a power amplifier 1 and the collector of the TR Q7 is connected to the non-inverting input of the amplifier 1. Further, the negative feedback resistor R2 is connected between the output and the inverting input of the amplifier 1 and the output terminal is connected to an output terminal T2.