PURPOSE: To effectively cool a pellet carrying disk by pressing a first and a second cryoheads into contact with the disk by the use of a driving means.

CONSTITUTION: A first and a second cryoheads between which a pellet carrying disk 3 stands and which face each other are arranged in the inside of a shield casing and a through hole is provided on the their center part. In a hollow outer shaft 90 in which the through hole is penetrated an end thereof is penetrated in a central shaft 9 connected to a flange 91 and a pressure chamber 8, an electro-magnet and its absorbent, a motor and a thrust bearing collar, a spring and the like composed of shape memory alloy as the driving means are connected to the other end. Therefore, a pellet carrying disk can effectively be cooled in simple formation without influencing pressing force on a casing and a heat escape.