PURPOSE: To realize the offset erasion by setting an offset cancel circuit between a non-inverted input terminal and an output terminal of a 1st operational amplifier.

CONSTITUTION: The capacity KC0 is connected between an output terminal of an operational amplifier A2 and a non-inverter operational amplifier A1 via switches 101 and 102. At the same time, the capacity LC0 is connected between the non-inverted input terminal of the amplifier A1 and an earth point. An input terminal V1 is added to an input terminal V1' which is connected to the earth pointvia a switch 103 and a sampling/holding circuit is added to an output terminal V2. Thus the electric charge charged to the capacity KC0 is inverted and distributed again between both capacities KC0 and LC0. In such a way, the offset can be erased.