In a pressure vessel (1) comprising a resin liner (2) provided with a tubular extension (22) defining a through hole therein for receiving and expelling the gas or liquid, a tubular member (100, 200, 300) fitted in the through hole of the tubular extension, a mouthpiece (4) threaded into the tubular extension, a fiber reinforced resin layer (3) placed around an outer surface of the resin liner, and a valve (60) fitted into the central bore of the tubular member, the valve include a section (62) having a smaller outer diameter than an opposing inner circumferential surface of the tubular member defining a gap between the valve and tubular member, and a resilient seal member (80) is placed in the gap. The tubular member is made of a material such as metallic material which is stiffer than the resin liner. Thereby, the resilient seal member is interposed between the tubular member and valve which are both highly stiff or free from deformation when the interior of the pressure vessel is placed under various pressure conditions so that the sealing performance of the resilient seal member can be ensured under all pressure conditions.