PURPOSE: To stabilize earlier an amplier circuit at application of power by connecting plural diodes from an output of a differential amplifier in parallel with a feedback resistor.

CONSTITUTION: A current chared in a capacitor 2 from an output of a differential amplifier 7 passes through diodes 81∼8n to the capacitor 2 not through a feedback resistor 4 at the application of power supply voltage, then the potential of the capacitor 2 is charged rapidly by the forward voltage VF of the diodes 81∼8n. Further, the ratio of the forward voltage VF of the diodes 81∼8n to a resistance volue Rf of the feedback resistor 4, that is, a current of VF/Rf passes through the feedback resistor 4 and then charged. Thus, the number of diodes 81∼8n, 91∼9n is adjusted in the operating voltage range, then high speed operation is attained. Thus, the time until the input bias voltage is made stable is quickend at application of power supply.