To provide an inexpensive structure for preventing deformation and rupture of a pressure vessel by discharging gas within the pressure vessel when an atmospheric temperature rises.

One or more vertical grooves 5 extending in the vertical direction beyond the sealing part are punched on an inner peripheral surface of an opening 2 of a container body 1. After solubilizing agent 6 melting at a prescribed temperature is filled into the vertical groove 5 to be flush with the inner peripheral surface of the opening 2, an outer peripheral surface of a flange 7 of a mountain cap 3 is brought into pressure-contact with the inner peripheral surface of the opening 2 and an outside surface of the solubilizing agent 6 by clinching.