INFRARED DETECTOR

PURPOSE:To quickly and surely set the visual field of an infrared ray detecting element for viewing the outside by making an aperture holding jig expandable and the distance between the opening of an aperture and the infrared ray detecting element changeable from the outside. CONSTITUTION:Infrared rays 7 entering through an infrared-ray transmissive window 2 are made incident on an infrared detecting element 8 through the opening section of an aperture 6a. When the distance between the opening section of the aperture 6a and the element 8 is adjusted by expanding or contracting a holding jig 5a at the time of incidence, the quantity of background radiation which irradiates the element 8 can be changed. The extending/ contracting length of the extending/contracting section of the jig 5a can be changed continuously in an interlocking way with a gear mechanism coupled with a motor 10 which is rotated by driving power supplied from a lead pin 11. Moreover, the magnitude of displacement is detected by means of a displacement meter 12.