A stopper member (12) is molded to a uniform thickness by press working, e.g., a copper-alloy thin plate material. The stopper member (12) has a through-hole (12H) constituting a part of an internal pressure release mechanism, the through-hole (12H) facing the outer peripheral surface of a guide part (18B). If the pressure in a hollow part (14) of the stopper member (12) rapidly increases to or beyond a prescribed value, the trunk part (middle part) of the stopper member (12) swells, whereby a liquid refrigerant in the hollow part (14) is easily released into the inner peripheral part (10a) of a tube body (10) through the through-hole (12H) in an open state.