PURPOSE: To prevent the deterioration of the function of a packing provided between a guide cylinder containing a fluid and a moving member.

CONSTITUTION: A thermal expansion body 1 thermally expanded/shrunk by the temperature change of a body to be detected is stored in a case 1, a fluid 4 is stored in a guide cylinder 5 connected to the case 2 so that the volume change of the thermal expansion body 1 is transferred via a diaphragm 3, and a moving member 6 is inserted into the guide cylinder 5 to be pressed and moved by the fluid 4 in this thermo-element. A guide cylinder contact section 7a and a moving member contact section 7b are provided between the guide cylinder 5 and the moving member 6, and a packing 7 having a recess 7c is provided between the guide cylinder contact section 7a and the moving member contact section 7b on the fluid 4 side.