The purpose of the present invention is to reduce vibration derived from a refrigeration machine. A cryostat comprises: a helium tank (2) which stores liquid helium; a refrigeration machine (5) which is provided above the helium tank (2) and re-liquefies the vaporized liquid helium in the helium tank (2); a cylindrical member (15) which houses the lower part of the refrigeration machine (5) and forms a liquefaction chamber (8) communicating with the helium tank (2); and a buffer tank (10) which stores helium gas and communicates with at least either the space above the surface of the liquid helium in the helium tank (2) or the liquefaction chamber (8). The gas-phase volumes of the helium tank (2) and the liquefaction chamber (8) increase by having the buffer tank (10) communicate with the helium tank (2) and the liquefaction chamber (8).
