To suppress the degradation of sealing property of a pressure vessel and the deterioration of a sealing member, and to reduce the workload and cost of manufacture, a blow molding device includes a pair of molds configured to be clamped to sandwich a parison from both lateral sides, and a blow pin configured to form a neck portion together with the molds. The blow pin includes a blow pin body portion having an outer circumferential surface of a shape corresponding to an inner circumferential surface of the neck portion, and a ring portion forming an annular recess portion between the blow pin body portion and the ring portion to form an outer circumferential surface of a tip portion of the neck portion, which is a smooth surface without any parting line.

To suppress the degradation of sealing property of a pressure vessel and the deterioration of a sealing member, and to reduce the workload and cost of manufacture, a blow molding device includes a pair of molds configured to be clamped to sandwich a parison from both lateral sides, and a blow pin configured to form a neck portion together with the molds. The blow pin includes a blow pin body portion having an outer circumferential surface of a shape corresponding to an inner circumferential surface of the neck portion, and a ring portion forming an annular recess portion between the blow pin body portion and the ring portion to form an outer circumferential surface of a tip portion of the neck portion, which is a smooth surface without any parting line.