PURPOSE: To enhance mass productivity while reducing manpower by realizing a preassembly of an infrared filter and a semiconductor substrate formed with an infrared detecting part.

CONSTITUTION: The infrared sensor comprises a semiconductor substrate 201 formed with an infrared detecting part 203 and an infrared filter part 212 for introducing infrared rays to the infrared detecting part 203 wherein the infrared filter part 212 is constituted of a silicon substrate 101 provided integrally on the surface of the semiconductor substrate 201. A cavity 210 is formed in a region corresponding to the infrared guide path from the infrared filter part 212 to the infrared detecting part 203 for at least one of the silicon substrate 101 and semiconductor substrate 201.