To guarantee long-term stability of a type of thermo sensor in which elastic strain energy is supported by junction fixation by a soluble material such as solder and in which the elastic strain energy of an elastic body is released and operated by fusion of the soluble material, and improve reliability of operation of a thermo protector using the thermo sensor.

This is the thermo sensor in which the elastic body 2 is made as a convex curved line shape because both ends 21, 22 are fixed to a body 1 in a state that the elastic body 2 is compressed in the longitudinal direction, in which one end side of the curved line is erected against the body 1 at a prescribed angle θ', in which the other end 22 of the same curved line is made as a bending angle 0, in which fixation of the one end part 21 of the elastic body and the frame body 1 is carried out via the soluble material 3, and in which the melting point or the softening point of the soluble material is made as the operation temperature.