To improve sensor measurement accuracy and obtain quick responsivity.

This sensor signal processing circuit is provided with a capacitance-type sensor part with characteristics which changes as a whole according to changes in a physical quantity to be measured, an electric power source part with at least two types of A.C. power sources with different polarities or phases, and an arithmetic part connected to the output side of the sensor part for performing arithmetic processing for obtaining the difference, ratio, etc., of signals due to sensor capacitance. The sensor signal processing circuit is provided with a part for synchronously detecting output signals of the arithmetic part by two types of A.C. signals with different polarities or phases, and measurement and responsivity in measuring physical quantities are heightened by the sensor signal processing circuit.