PURPOSE: To compensate the measuring temperature versus converting voltage characteristic of an input signal by providing a nonlinearity compensating circuit using a Zener diode to an input circuit of an operational amplifier.

CONSTITUTION: The measured output of a temperature measuring circuit 1 is amplified at an amplifier circuit 9 and inputted to a linearizing circuit 10. Said linearizing circuit 10 has an operational amplifier 25, a series circuit comprising resistors 28, 29 and a Zener diode 30 is connected to the 1st input and a circuit comprising resistors 26, 27 and a Zener diode 31 connected between a connecting point of the resistors and ground is connected to the 2nd input. An input signal is impressed to a connecting point between the resistors 28 and 26. Thus, the measuring temperature versus converting voltage characteristic of the input signal is compensated and linearized by the circuit comprising the Zener diode and the resistors, and a compensated output is obtained between terminals 23 and 32.