PURPOSE: To use an inexpensive aluminum electrolytic capacitor instead of an expensive tantalum capacitor by connecting serially two resistances between the output terminal of a second operational amplifier and an electric power source and connecting the connecting point of these resistances to the non- inverting input terminal of first operational amplifier.

CONSTITUTION: When an off-setting voltage between the input terminals of the first and the second operational amplifiers 1 and 4 are Vos1 and Vos2, an output voltage Vo, e, the voltage to occur at the non-inverting input terminal of the first operational amplifier 1 is e1 and an electric power source voltage is Vcc, the Vo, e comes to be formulas I and II. As the result, an off-setting voltage Vo to occur at the output terminal of the first operational amplifier 1 comes to be only the off-setting voltage Vos2 of the second operational amplifier 4. A voltage (e) to occur at the output terminal of the second operational amplifier 4 is sufficiently largely obtained to the Vos1 and the Vos2, and can be made into an optional size by assembling suitably respective resistance values. Consequently, between both edges of a capacitor 6 connected to the feedingback circuit of the second operational amplifier, the sufficient bias voltage can be generated.