PURPOSE: To improve the detection sensitivity, by providing resistors, whose resistance values are changed in accordance with strain, in both end parts of a narrow band-shaped arm supporting a pressure receiving part of a pressure receiving diaphragm.

CONSTITUTION: The pressure sensor is constituted with a case 18 in which a thick hollow disc-shaped packing 14, a pressure receiving diaphragm 15, a holder 16, a cover 17, and incidence windows 19 and 20 are provided and a measuring component gas is sealed. The pressure receiving diaphargm 15 has a pressure receiving part 28 which is surrounded with space parts 22, 23, and 24 formed by cutting a thin plate such as a quartz plate 21 and is supported by three narrow arms 25, 26, and 27, and resistors consisting of resistance materials such as nickel chromium are stuck to both end parts of the arm 25 by the sputtering technique or the like, when infrared rays are made incident into the case 18, the pressure in the case 18 is increased to press the pressure receiving diaphragm 15 upward in the direction of an arrow, and the arm 25 is deformed to give a strain to resistors, and their resistance values are changed.