The infrared sensor (1) includes a base (10), and an infrared detection element (3) formed over a surface of the base (10). The infrared detection element (3) comprises an infrared absorption member (33) in the form of a thin film configured to absorb infrared, and a temperature detection member (30) configured to measure a temperature difference between the infrared absorption member (33) and the base (10). The temperature detection member (30) includes a p-type polysilicon layer (35) formed over the infrared absorption member (33) and the base (10), an n-type polysilicon layer (34) formed over the infrared absorption member (33) and the base (10) without contact with the p-type polysilicon layer (33), and a connection layer (36) configured to electrically connect the p-type polysilicon layer (35) to the n-type polysilicon layer (34). Each of the p-type polysilicon layer (35) and the n-type polysilicon layer (34) has an impurity concentration in a range of 1018 to 1020 cm−3. The p-type polysilicon layer (35) has its thickness of λ/4n1p, wherein λ denotes a center wavelength of the infrared to be detected by the infrared detection element (3), and n1p denotes a reflective index of the p-type polysilicon layer (35). The n-type polysilicon layer (34) has its thickness of λ/4n1n, wherein n1n denotes a reflective index of the n-type polysilicon layer (34).