A pretensioner is provided, which can be partially changed in mechanical strength of in a cylinder, in addition, can be widely used. In the pretensioner, the cylinder is molded by forging, and a positioning portion as a high-strength portion is formed from a partition formed using a excess portion produced during the forging-molding. Therefore, while an outer circumferential shape of the cylinder is not changed, a specification of the positioning portion can be varied, the specification including a formation position of the positioning portion, an extension dimension of the positioning portion from the cylinder, and thickness of the positioning portion along a through direction of the cylinder.