Abstract: To perform an even, high temperature baking treatment at about 450.degree. C. to a cryopump for the achievement of an extremely high vacuum, the cryopump is divided into two, a pump section P and a refrigerator R; the pump section P is cut off, with a vacuum state maintained, from the refrigerator R; and cooling stages 49 and 69 of the refrigerator R are connected through detachable heat transfer means 53 and 73 to cryopanel 2 and 5 of the pump section P, whereby the pump section P and the refrigerator R being detachably connected together. A drive unit of the refrigerator R and a casing 1 of the pump section P are connected together by a bellows 36, and at least a part of the transfer means 53, which connects the cooling stage 49 and 69 of the refrigerator R to the cryopanels 2 and 5 of the pump section P, made of a flexible material.