To shorten a time for regeneration by directly heating, by an inner heater, an expander for expanding a high pressure refrigerant gas from a compressor part and a pump body enclosing a cryoarray, in a regeneration step.

In a pump acting part 52, primary and secondary cryoarrays are connected to an expander for expanding high pressure helium, and they are enclosed and shut-out from an outer environment by a pump body 56. An inner heater 61 is arranged on the pump body 56 by being brought into contact with a body outer surface. When the pump acting part 52 is regenerated, nitrogen gas heated to about 120°C by a heater 26 is supplied from a purge tube 60 until the cryoarray exceeds a normal temperature. Simultaneously, the pump body 56 is directly heated by the inner heater 61. As a result, a temperature of the pump acting part 52 is raised to the normal temperature at a short time, and regeneration is carried out. Especially, a material which is condensed to the pump body 56 is gasifyed easily and is exhausted.