PURPOSE: To enable an object to be fitted without being damaged regardless of a size and a shape of the object by sealing a connection part between a site for attraction of a magnet and a thermal sensor body in one piece.

CONSTITUTION: A thermal sensor body 1 is engaged to a groove 9b which is provided at a plane part 9a for attraction of a magnet member 9, an outer surface of the sensor body 1 is set to a same plane as that of a plane part 9a, and then a copper tape 10 is wound, thus enabling both to be constituted in one piece. A shape memory site 5 is set to both sides of a mounting part of the member 9 so that the sensor body 1 recovers shape by bending its free edge part to a side of the member 9. Then, the plane part 9a is allowed to contact an iron and steel product to be detected for attraction by a magnetic force, thus enabling the object to be fitted without being damaged regardless of a shape and a size of the object.