PURPOSE: To freely and simply pull down a heat sink by a method wherein the heat sink is fixed by a cavity provided in a plate spring and the heat sink or a stud and further a pulling-out jig is used.

CONSTITUTION: A plate spring 5 fitted into a stud 4 is engaged with a cavity 7 inside a hole of a heat sink 6 and the sink 6 is pushed against a heat transfer plate 2 by the spring 5, whereby the sink 6 is fixed. The sink 6 comes into contact with the plate 2 by the spring 5 and the cavity 7 to fix each other, whereby heat generated in a semiconductor element 3 can be radiated into an atmosphere through the sink 6. Further, when a pulling-out jig 10 is inserted into a gap 8 between the stud 4 and the sink 6, the spring 5 is so fitted as to spring out to a side face of the stud 4, and the spring 5 is pushed in above the side face of the stud 4 by the jig 10 to detach from the cavity 7. Thereafter, if the sink 6 is picked up, it can easily be separated from an LSI case 1. Thus, the sink 6 can freely and simply be pulled down.