Infrared detector and gas analyzer

When first and second PbSe detectors 6 and 7 are irradiated with intermittent infrared radiation from a light source 3, infrared radiation detection circuits 21a and 21b output electrical signals in accordance with the magnitude of the infrared radiation, respectively. The output signals are supplied as they are to a CPU 32 via A/D converter 31, and, on the other hand, AC signals of the output signals via AC components detection circuits 22a and 22b reach the CPU 32. The CPU 32 corrects the AC signals, based on data which relates to the resistances and sensitivities of the PbSe detectors 6 and 7 and which are stored in an EEPROM 23, and the DC components of the output signals of the infrared radiation detection circuits 21a and 21b.