PURPOSE: To prevent occurrence of tension or looseness on a support member which may caused by thermal contraction generated at the time of shifting of an inner vessel from a normal temperature condition to an extreme low temperature condition by specifying a position of an installation point of a support member on an outer vessel which houses the inner vessel for housing an extreme low temperature coolant under an adiabatic condition.

CONSTITUTION: A cryostat has a cylindrical inner vessel 11 which houses an extreme low temperature coolant, and an outer vessel which houses the inner vessel 11 through a vacuum space in an adiabatic condition. An adiabatic sealed layer 15 is formed between the vessels 11 and 13, while a multilayer adiabatic layer 17 is formed between the adiabatic sealed layer 13 and the outer vessel 13. The inner vessel 11 is supported to a specified position inside the outer vessel 13 by means of a bar-like support member 19. In installation of the support member 19, a support member installation point on the outer vessel 13 is arranged such that a distance between the support member installation point on the inner vessel 11 and the support member installation point on the outer vessel 13 under a normal temperature is equal to that under an extremely low temperature.