To ensure the long-term stability of a heat sensitive element of non-return type having as an operating source the stored elastic strain energy of an elastic material.

The elastic materials 11, 12 are held in the shape of storing elastic strain energy by unifying a fusible material 3 with the surfaces of the elastic materials. Softening or melting of the fusible material 3 releases the strain energy, whereby the elastic materials 11, 12 are deformed. The elastic strain needs to be held for the elastic materials 11, 12 to store the elastic strain energy. Since the fusible material 3 is integrated with the elastic material surfaces to hold the elastic strain, the stress exerted on the large interface between the elastic materials 11, 12 and the fusible material 3 can be distributed, thereby suppressing the creep of the fusible material and ensuring the long-term stability of the thermally sensitive element.