PURPOSE: To suppress a detection error due to the influence of ambient temperature by providing a feedback circuit which feeds the output of a bridge circuit back to the bridge circuit through a compensating resistance.

CONSTITUTION: The resistance value of the temperature measuring resistance 3 at one branch of the bridge circuit 8 is R0 when its temperature is 0°C, and the circuit 8 enters a balanced state to generate an output voltage of 0V at an output terminal 7, but if the temperature rises or falls, the temperature measuring resistance 3 increases or decreases in resistance value and the circuit 8 becomes unbalanced. If this enters the balanced state, the output voltage EOB corresponding to variation in the resistance value of the temperature measuring resistance 3 is developed at the output terminal 7, but when a part of the output EOB is added to the voltage Er of the reference voltage source 6 of the circuit 8 by an adding circuit 12, the voltage of the reference voltage source 6 is elevated equivalently in proportion to the temperature variation and the output EOB of the circiut 8 varies with temperature according to a hyperbolic curve, which is approximated to the temperature characteristics of the thermocouple by selecting the value of each resistance properly.