To obtain a gas detector applicable to a situation where the ambient temperature varies over a wide range without sacrifice of measuring accuracy by setting the reference voltage of a differential amplifier automatically depending on the temperature sensor output.

Output from a bridge circuit constituted of a gas sensor 1 and fixed resistors 3, 4 is delivered to a differential amplifier circuit 6. A converter 8 converts a temperature sensor 2 output into a corresponding electric signal being applied to the circuit 6 as a reference voltage. More specifically, reference voltage of the differential amplifier circuit 6 is set automatically depending on the temperature sensor 2 output. The sensor 2 output is A/D converted and fed through the circuit 6 to a microcomputer 5 where specified operations are effected. When reference voltage of the circuit 6 is set automatically depending on the sensor 2 output, entire range of the A/D converter can be assigned to gas sensitivity and a situation where the ambient temperature varies over a wide range can be dealt with without sacrifice of measuring accuracy.