PROBLEM TO BE SOLVED: To avoid generation of expendables when sealing is released, thereby reducing running costs for key management.SOLUTION: A movable part (2) and a body part (3) are configured to be separate from a key holder. As a result of displacement of a relative position of the movable part (2) relative to the body part (3), a state where a ring end part (1a) is sealed and a state where the sealing of the ring end part (1a) is released can be switched.