PURPOSE: To easily control the amount of sublimation of solid carbon dioxide, and to control the effect of freezing easily in accordance with changes of external conditions by a method wherein the area of a non-thermal-insulation part of an external cylinder is adjusted by making a porous cylinder slide inside an internal cylinder, and the amount of heat from the non-thermal-insulation part is transmitted to the solid carbon dioxide through the porous cylinder.

CONSTITUTION: An internal cylinder 1 is inserted into an external cylinder 2 so that it can slide inside. The external cylinder 2 is equipped with an opening 8 at its bottom for releasing carbonic acid gas produced by sublimation of solid carbon dioxide, and a porous cylinder 6 is fixed to a bottom plate 10. The area of a non-thermal-insulation part on the lower side of the external cylinder 2 is adjusted by moving a handle 3 of the internal cylinder 1 upward and downward by hand with positioning grooves 9, 9' in an appropriate number provided to the internal surface on the upper side of the external cylinder 2 used as criteria, and the amount of sublimation of solid carbon dioxide can be adjusted by adjusting the amount of heat from the non-thermal-insulation part. Similar effect can be achieved by making the porous cylinder 6 slide inside the internal cylinder 1.