A heat sensor (1) includes: a housing (10) of a cylindrical shape having a bottom part (11); and a heat detection unit (30) configured to detect heat of gas, wherein the housing (10) has a first hole (21) and a second hole (22) from one side of which gas flows in and from another side of which the gas flows out. The heat detection unit (30) is arranged in a peripheral region (10b) different from a center (10a) of the housing (10) when the heat sensor (1) is viewed from a central axis (J1) of the housing (10).