A secondary battery includes: a case having an opening; an electrode assembly in the case; a cap plate for sealing the opening of the case; and an electrode unit penetrating through the cap plate, and electrically coupled to the electrode assembly. The electrode unit includes: a current collector coupled to the electrode assembly; and a lead coupled to the current collector and penetrating through the cap plate. The current collector and the lead are coupled to each other by inserting an assembling portion of the lead into an accommodation opening formed in the current collector. Thus, a structure of a coupling portion of the electrode unit for forming charging/discharging paths coupled to the electrode assembly may be improved, and accordingly, an effective internal volume of a case in which the electrode assembly is accommodated and a battery capacity of the electrode assembly may be increased.