PURPOSE: To secure a sufficient contact-parting distance for a first plate spring.

CONSTITUTION: An inversion spring 4 which is inverted according to the amount of displacement of a thermally-actuated element 3, a first contact part 50 comprising the end of the inversion spring 4 and a first plate spring 38 opposed to the end of the inversion spring 4 in such a way as to freely make contact with and separate from the end, an interlocking member 7 which operates on inversion of the inversion spring 4, and a second contact part 51 having a second plate spring 33 opened and closed by the interlocking member 7, are all enclosed in a body 1. The body 1 is provided with a position-limiting projection 52 for positioning the first plate spring 38 along the direction of the inversion spring 4 while the end of the inversion spring 4 does not abut to the first plate spring 38.