PURPOSE: To prevent concentration of stress at a junction portion and enhance the strength of the junction portion and prevent the junction portion from being cracked by forming mutually fitting projecting and recessed portions respectively on the junction face of a casing and that of the cylinder of a cold air generating device which is disposed inside the casing and cooled.
CONSTITUTION: An extreme low temperature refrigerator 1 comprises a refrigerator unit 5 adapted for compressing a refrigerant gas and disposed outside a casing 4, and a cold air generating device 6 disposed inside the casing 4 to cool a compressed refrigerant. In this case, the cold air generating device 6 comprises a displacer 15 disposed inside a cylinder 14 in such a manner as freely reciprocating and sliding inside the cylinder 14, and a cold head 16 disposed on the outer periphery of the cylinder 14. A projecting portion 22 is formed on the outer periphery of the cylinder 14. A recessed portion 23 is formed in the inner periphery of a flange portion 13 inside the casing 4. The projecting portion 22 is fitted into the recessed portion 23 to thereby join the cylinder 14 and the flange portion 13 to each other.
NISHIJO TOKUJI
MURAYAMA SHIGERU
