To obtain a thermo-element for effectively increasing wax sealed in a casing in temperature for all obtaining a secure seal structure and providing a secure seal structure at a terminal extracting part of a terminal for current- carrying control to a heating means.

There are provided with a thermal expansion body 4 inserted in a cylindrical cases 2 and 3 for forwarding and retreating an action piston 7 to/out of the cases with changing in volume accompanied with changing in temperature and a heating element 12. The heating element is almost cylindrical shape, and arranged as laid in the thermal expansion body at almost center position. An electrode member 13, connected to external electric source via the terminal extracting part 5 installed at an end part of a counter piston side of the case is arranged inside the heating element. A plate spring material 14 sharing a radiation fin for radiating for the thermal expansion body is arranged between the outside of the heating element and an inner wall part of the case. The plate spring material has greater surface area than that of the heating element.