PURPOSE: To obtain an amplifier circuit which operates at a high speed and is small in an energy consumption by providing four switches at an operational amplifier circuit.

CONSTITUTION: Switches S1-S3 between an input terminal 1 and one edge of a first capacitor C1, between one edge of the first capacitor C1 and a reference voltage source 3 and between other side terminal of the first capacitor C1 and a reference voltage source 4, an operational amplifier A in which the inverting input terminal is connected to other side terminal of the first capacitor C1 and a normal rotation input terminal is connected to a reference voltage source 5, a second capacitor Cf in parallel between the inverting input terminal and the output terminal of the operational amplifier A and a fourth switch Sf are provided. At the time of the sampling of an input voltage, a switch S1 is closed and when the charge is accumulated on the capacitor C1, a switch S3 is also simultaneously closed. Thus, the time necessary to supply the charge on the C1 is not limited by the output current of the operational amplifier and the amplifier circuit can be operated at a high speed.