Jig for welding cap plate of secondary battery

Provided is a jig for breaking the case of a secondary battery to weld the case and the cap plate of a secondary battery, thereby preventing the deterioration of performance and lifetime due to the inferior welding. A jig comprises a plurality of clamp members(20,21,22) which are arranged along the welding pathway of a case(11) and a cap plate(13) to break the case and the cap plate; and operation cylinders(23,24,25) which are connected with the each clamp member to apply the clamping pressure to the each clamp member indivisually. Preferably the case and the cap plate are welded by laser welding method, and the operation cylinder has the structure that the clamping pressure increases gradually along the welding propagation direction.