PURPOSE: To obtain a cryostat which facilitates the smooth exhaust of vaporized gas from a coolant vessel and facilitates the elimination of a pressure which causes a natural convection in a linkage pipe and permits very little heat invasion.

CONSTITUTION: In order to prevent heat invading from the outside through a linkage pipe 12 which is installed in a cryostat by piercing through the chamber from reaching vaporized gas, a convection blocking cylinder 14 made of heat insulating material is tightly inserted into the linkage pipe 12 and, further, an exhaust hole 15 for the vaporized gas is provided in the convection blocking cylinder 14.