PURPOSE: To obtain a distortion gage of a compact size, a small consuming current and an easy maintenance automatically erasing unbalanced components of resistance and capacity at the initial time of the measurement, which are generated at the detecting part, by an electrical circuit.

CONSTITUTION: The right side of a part in the drawing indicated by which is connected to a detecting part A such as a Wheatstone bridge or the like by means of four core shielded cables. The output signal from the detecting part A is received by an input transformer T1, and the loop of a resistance R is formed by a carrier amplification circuit B, a resistance component detecting circuit, a carrier filter circuit C, a DC amplification circuit E, a circuit F for controlling and holding the amplitude of the carrier in correspondence to the DC voltage and a circuit G for erasing the unbalance at the initial period of resistance components. Further, the loop of capacity C is formed by a carrier amplification circuit B, a capacity component detecting circuit, a carrier filter circuit D, a circuit H for driving the circuit for erasing the capacity unbalanced components, and a circuit I for erasing the capacity unbalanced components. As described above, a gage of a small size and a small consuming current can be obtained without using any mechanical potentiometer.