PURPOSE: To eliminate the influence of the distributed capacities with simple constitution by connecting the excitation signal from a signal source to one stationary electrode of a differential type capacity sensor, and connecting the same to the other stationary electrode via an inverter.

CONSTITUTION: The excitation signal from a singnal source SG of low output impedance is applied to the stationary electrode terminal A of a differential type capacity sensor via an inverter IN of low output impedance. As an antiphase relation with this, the output of the signal source SG is applied to a stationary electrode terminal B. On the other hand, the output of the differential amplifier A is connected to the case F of variable electrostatic capacitors C1, C2 constituting the differential capacity sensor. Since the output and inverted input of the amplifier A are directly connected, the same voltage is applied between the movable electrode terminal D and the case F; therefore, the existence of a distributed capacity CS3 is negligible. Hence, the influence of distributed capacities CS1WCS3 is completely eliminated, and linear conversion characteristics are obtained. Also, stable and sure conversion characteristics are obtained.