A secondary battery comprising an electrode assembly including at least two electrode plates and a separator interposed between the electrode plates, and a battery case containing the electrode assembly being impregnated with an electrolytic solution, wherein each of the electrode plates includes: an electrode body including a collector having one surface or opposite surfaces to which an electrode mixture containing an electrode active material is applied, and at least one electrode tab extended externally from a side of the electrode body and including a collector to which an electrode mixture is not applied; and indented portions (311, 313) that are formed from lower ends of opposite sides of the at least one electrode tab in an opposite direction to an externally extending direction of the at least one electrode tab in a side of the electrode body in which the electrode tab externally extends, wherein the at least one electrode tab of the electrode plates is coupled to an electrode lead including a positive electrode lead and a negative electrode lead, wherein one end portions of the positive electrode lead and the negative electrode lead protrude to an outside of the battery case, wherein the battery case includes a concave-shaped accommodating portion for accommodating the electrode assembly and a sealing portion formed in an external circumferential surface of the accommodating portion to secure a sealing property of the battery case, wherein the sealing portion is positioned at an upper side portion of a welded portion between electrode tabs and the electrode lead, and wherein a side of the accommodating portion is positioned at a lower end portion of the welded portion between the electrode tabs and the electrode lead. an electrode body including a collector having one surface or opposite surfaces to which an electrode mixture containing an electrode active material is applied, and at least one electrode tab extended externally from a side of the electrode body and including a collector to which an electrode mixture is not applied; and indented portions (311, 313) that are formed from lower ends of opposite sides of the at least one electrode tab in an opposite direction to an externally extending direction of the at least one electrode tab in a side of the electrode body in which the electrode tab externally extends, wherein the at least one electrode tab of the electrode plates is coupled to an electrode lead including a positive electrode lead and a negative electrode lead, wherein one end portions of the positive electrode lead and the negative electrode lead protrude to an outside of the battery case, wherein the battery case includes a concave-shaped accommodating portion for accommodating the electrode assembly and a sealing portion formed in an external circumferential surface of the accommodating portion to secure a sealing property of the battery case, wherein the sealing portion is positioned at an upper side portion of a welded portion between electrode tabs and the electrode lead, and wherein a side of the accommodating portion is positioned at a lower end portion of the welded portion between the electrode tabs and the electrode lead.