An electric energy storage device in which a cell assembly having electrode leads is installed in a metal case, the electric energy storage device comprising: an internal terminal formed with a support, connection ribs and empty spaces so that lower surfaces of the support and the connection ribs come into contact with a part of the electrode leads, and an external terminal, being exposed to the outside, and being in contact with the internal terminal, which is disposed inside the metal case, wherein the electrode leads include a first part compressed by the support and the connection ribs of the internal terminal and a second part inserted into the empty spaces of the internal terminal to maintain a shape thereof, wherein the electrode leads are cut at a border portion of the first part and second part, corresponding to both side surfaces of the connection ribs by a cutting device, wherein upper ends of the second part of the electrode leads inserted into the empty spaces of the internal terminal are positioned higher than an upper surface of the internal terminal, at the same point as the upper surface of the internal terminal, or lower than the upper surface of the internal terminal, wherein the support is located at a center of the internal terminal, wherein the connection ribs are arranged at a periphery of the support at regular intervals with a rod shape to extend radially, wherein the plurality of connection ribs have flanges formed at ends thereof to correspond to inner wall of the metal case, wherein the flanges wrap a lower edge of the external terminal, wherein an upper end of the metal case is curled inward to fix the external terminal, wherein a contact area of the internal terminal, which comes into contact with the electrode leads, is 60% or above of an entire sectional area of the electrode leads. an internal terminal formed with a support, connection ribs and empty spaces so that lower surfaces of the support and the connection ribs come into contact with a part of the electrode leads, and an external terminal, being exposed to the outside, and being in contact with the internal terminal, which is disposed inside the metal case, wherein the electrode leads include a first part compressed by the support and the connection ribs of the internal terminal and a second part inserted into the empty spaces of the internal terminal to maintain a shape thereof, wherein the electrode leads are cut at a border portion of the first part and second part, corresponding to both side surfaces of the connection ribs by a cutting device, wherein upper ends of the second part of the electrode leads inserted into the empty spaces of the internal terminal are positioned higher than an upper surface of the internal terminal, at the same point as the upper surface of the internal terminal, or lower than the upper surface of the internal terminal, wherein the support is located at a center of the internal terminal, wherein the connection ribs are arranged at a periphery of the support at regular intervals with a rod shape to extend radially, wherein the plurality of connection ribs have flanges formed at ends thereof to correspond to inner wall of the metal case, wherein the flanges wrap a lower edge of the external terminal, wherein an upper end of the metal case is curled inward to fix the external terminal, wherein a contact area of the internal terminal, which comes into contact with the electrode leads, is 60% or above of an entire sectional area of the electrode leads.