PURPOSE: To prevent the deterioration of the operation precision of a thermo- wax device by sticking opening section end faces of a case and a cover at the periphery outside of a diagram with an adhesive having a three-layer structure.

CONSTITUTION: A thermo-wax device has a case 1, a diaphragm 2 and a cover 3. The opening section end face of the case 1 and the opening section end face of the cover 3 are stuck at the periphery outside of the diaphragm 2 with an adhesive 9. This adhesive 9 has a three-layer structure consisting of an intermediate layer 9a made of a high-elasticity adhesive and high-strength adhesives laminated on both sides of the intermediate layer. Even if the increase and decrease of the inner pressure of the thermo-wax device are repeated, the intermediate layer 9a is elastically deformed and absorbs distortion. The periphery of the diaphragm 2 is prevented from infiltrating into the gap, the protruded quantity of a piston rod is not changed, and the deterioration of the operation precision of the thermo-wax device can be prevented.