PURPOSE: To reduce noise to the utmost by forming a switched capacitor integrator of a switch, a capacitor and a differential amplifier.

CONSTITUTION: When an input signal VIN is inputted to an input terminal 1 and a clock 1 reaches a high level and a clock 2 reaches a low level, switches 4, 6 are turned on, switches 5, 7 are turned off and a changer (VIN.C12) is stored in a capacitor 12, and both electrodes of a capacitor 13 are connected via ground 17. When the clock 1 reaches a low level and the clock 2 reaches a high level, the charges (VIN.C12) stored in the capacitor 12 is integrated by a capacitor 14 and a charger (VIN.C13) is stored in one electrode of the capacitor 13 and a charge (-VIN.C13) appears in the other electrode and the charge is integrated by a capacitor 15.