PURPOSE: To obtain an output corresponding to the load to be measured by the same constitution of a circuit in the case where an electrode having a pair of capacities or one capacity is displaced due to the load to be measured, by detecting the current of a value proportional to the difference between the respective reciprocals of a pair of electrostatic capacities.

CONSTITUTION: At least one of electrostatic capacities C1 and C2 in a pair is changed in correspondence with the mechanical displacement, while the voltages corresponding respectively to C1 and C2 are transduced into pulse signals i1 and i2. And, each of the negative feedback circuits of negative feedback amplifiers Q3 and Q4 is intercepted intermittently. In tis way, the voltages V1 and V2 proportional to the respective reciprocals of C1 and C2 are formed and the difference voltage Vo between the voltages is taken out through the intermediary of Q5 and a transitor 5.