An amplifier circuit includes a main amplifier and an auxiliary circuit that improves a slew rate of the main amplifier. The main amplifier is composed of a one-stage CMOS amplifier, amplifies a voltage difference between two input signals, and outputs, from output terminals, an output signal corresponding to the voltage difference of the input signals. The auxiliary circuit controls an auxiliary bias current flowing through the output terminals according to the voltage difference of the input signals, and interrupts the auxiliary bias current at a predetermined timing before completion of settling. Such a scheme enables improvement of a slew rate by the auxiliary circuit and high-speed operation as well as reduction of error due to mismatch between the main amplifier and the auxiliary circuit, thereby yielding high-accuracy output signal output therefrom.