PURPOSE: To reduce the heat capacity of a heat-sensitive element and to improve heat responsiveness by forming a freely movable air layer around the heat-sensitive element and forming a cover consisting of a molded resin around the air layer.

CONSTITUTION: An drawing electrode 8 of the heat-sensitive element 1 and a core 2 of a twisted wire 4 are caulked and connected by a caulking terminal 16. The freely movable air layer M is formed around the heat-sensitive element 1 and the resin cover 17 molded with a resin is formed on the outside of the air layer M. A penetration hole 18 for ventilation is arranged on a position opposed to the heat-sensitive element 1 on the wall surface of the resin cover 17. The resin cover 17 has a cylindrical part 2 arranged with a pitch size almost equal to the bending size of the drawing electrode 8 of the heat-sensitive element 1 and the twisted wire 4 is inserted into the cylindrical part 2.