To provide a new wax thermosensitive element allowing the dissolution of problems in both a sleeve-type wax thermosensitive element and a diaphragm- type wax thermosensitive element.

In this wax thermosensitive element, a guide tube body 6 is fixed to the upper end of a bottom-equipped tube-like vessel 1 sealed with a wax thermosensitive body 11 by caulking, while a piston 10 is movably inserted in an internal diameter part 7 of the guide tube body 6. A long, flexible, upwardly-bulging and bag-like sleeve 9 is provided inside the internal diameter part 7 of the guide tube body 6 such that the upper end of the sleeve 9 contacts with the lower end of the piston 10, and the lower end periphery 13 of the sleeve 9 is sandwiched and fixed between the upper end face of the vessel 1 and the lower end face of the guide tube part 6.