PURPOSE: To reduce the deterioration of precision against the variation of supply voltage or a noise by setting a chopper control signal so that the potential amplitude of the chopper control signal to be impressed to the gate of a transistor has a period shorter than the difference of the current potential of an inverter and earth potential during the shortcircuit period of the input point and the output point of the inverter.

CONSTITUTION: The chopper control signal Tc is set so that the potential amplitude of the chopper control signal Tc has the period shorter than the difference of the supply potential Vcc of the inverter 1 and the earth potential during the shortcircuit period of the input point 7 and the output point 8 of the inverter 1. In case that the variation arises in the supply voltage Vcc, since the gate potential of a chopper transistor 2 is V1 (V1<Vcc), impedance is high, and a signal feedback function from the output point 8 to the input point 7 becomes very small, and it becomes the feedback function V'7 (V'7<<V7). Thus, since offset quantity at the time when the chopper control signal Tc is disconnected is very small, in case that afterwards, a signal to be amplified is transmitted to the input point 7, it can be amplified at good precision.