Disclosed herein is a secondary battery including an electrode assembly, having pluralities of electrode tabs joined to electrode leads, mounted in a receiving part of a battery case, wherein the battery case has concave steps formed at the inner upper end of the receiving part thereof between electrode tab-electrode lead coupling portions (a cathode terminal portion and an anode terminal portion) of the electrode assembly and at the inner opposite sides of the receiving part thereof corresponding to the opposite sides of the electrode assembly such that the electrode assembly is in tight contact with the concave steps.