Provided is a cryocooler configured to be mountable on a vacuum container to cool a liquid refrigerant container. The cryocooler includes an attachment flange forming a refrigerant gas chamber between a mounting port of the vacuum container and the attachment flange when the cryocooler is mounted on the mounting port, and movable in a detachment direction by raising a pressure of the refrigerant gas chamber, and a cooling stage cooling an object to be cooled disposed inside the vacuum container and movable from a cooling position in contact with the object to be cooled to a non-cooling position separated from the object to be cooled in response to a movement of the attachment flange in the detachment direction. The refrigerant gas chamber is connected to the liquid refrigerant container.