To easily fix heat insulation elements having different thicknesses with a simple and inexpensive constitution by a small force.

This fixing device is constituted of a receptacle 1 fixing a heat insulation element 13 to a structural part B, a a head 2 having a large surface, and a shaft 3 projecting from the receptacle 1 and further a pressure member 4 with a through hole at the center. In the fixing device having incisions 5, 6 engaged with each other in the shaft 3 and the housing 1, a stud-shaped expanding element 8 which can be driven in the central through hole 7 of the pressure member 4 is provided and further, at least one longitudinal slit 9 is formed in the shaft 3. The longitudinally extending slit 9 is extended from a loose end of the opposite side to the head 2 having a large surface of the shaft 3 to at least a part of the length L1 of the shaft 3.