To significantly reduce a differential heat sensor in size only by a mechanical structure.

The heat sensor 10 includes a package 12 having a package chamber which receives external heat and is shielded from air, and a sensor chip 20 contained in the package chamber 16. The sensor chip 20 includes: a chip displacement unit 22 having a membrane portion 26 which is displaced according to pressure change of the package chamber 16; a chip contact unit 24 which is in close contact with the chip displacement unit 22 and has a shielded contact chamber 28 formed therein; normally opened contacts 30, 32 which are placed in the contact chamber 28 and closed due to displacement of the membrane portion; a venthole 38 exposing the contact chamber 28 to the outside; and a leakage structure 40 which leaks air in the package chamber to the outside through a venthole 38 to suppress the pressure change when outside air temperature gradually rises.