To provide a differential heat detector capable of replacing a part to connect an inspection pipe to a leak hole and a part having the leak hole without taking an assembled part apart.

In the differential heat detector including: a leak part 5 that has a leak hole 5c communicating inside and outside an air chamber 3 and is placed on the upper wall of the air chamber 3; and a pipe connecting structure 7 that is placed above the leak part 5 and has an internal passage 8c to connect an inspection pipe P to the leak hole 5c air-tightly when the inspection pipe P is connected, the pipe connecting structure 7 includes a cover 8 that is placed on the base 2, presses the leak part 5 from above and through an opening 2b formed above the leak part 5 in the base 2, and thus connects the internal passage 8c to the leak hole 5c air-tightly.