PURPOSE: To set the temperature and pressure within the vessel at a value less than a defined value to prevent the escape of the coolant by forming the end part of the vessel for sealing and enclosing a coolant for cooling an electronic apparatus or the like into a curvature shape and providing a plug having a melting point lower than that of a material for the vessel at a part of the vessel.

CONSTITUTION: The end part 1' of the vessel 1 is formed into a curvature shape, and a plug 3 made of a material having a melting point lower than that of the vessel 1 is applied to a small hole 2. By this construction, even when an inner pressure is generated in the vessel, the end part 1' undergoes no deformation unlike the case of the conventional vessel 1. Therefore, there is no possibility that any gap is generated between the small hole 2 and the plug 3. The coolant sealed in the vessel 1 prevent from escaping out.