A method of manufacturing a stacked/folded type electrode assembly by using a folding device comprising: (a) manufacturing a plurality of unit cells (121, 122, 123, 124) including a positive electrode, a negative electrode, and a separator, and arranging the unit cells (121, 122, 123, 124) on a separator film in a long sheet form to manufacture a web in which plate type unit cells are arranged on an upper surface of the separator film at predetermined intervals, so that the unit cells are sequentially stacked with the separator film interposed therebetween; (b) vertically bending a surplus winding end portion by moving upward a pair of rollers located on a boundary between the surplus winding end portion of the separator film, and a first unit cell of a winding start portion, which is arranged in a state of being spaced apart from a winding end portion of the separator film in the web, and moving the pair of rollers in a direction of the first unit cell to horizontally bend the surplus winding end portion, and said pair of rollers includes a first roller located at a relatively upper portion and a second roller located at a relatively lower portion in a process of horizontally bending the surplus winding end portion; (c) pressing the horizontally bent surplus winding end portion of the separator film on the first unit cell after interposing the web between the pair of rollers; and (d) winding by rotating a mandrel including one or more grippers composed of one or more upper legs configured to fix an upper surface portion of the first unit cell and one or more lower legs configured to fix a lower surface portion of the separator film corresponding to the upper legs so that the unit cells (121, 122, 123, 124) are sequentially stacked with the separator film interposed therebetween, characterized in that the first roller and the second roller move upward to vertically bend the surplus winding end portion upward in a state of being positioned close to a boundary between the first unit cell and the surplus winding end portion of the separator film at a lower portion of the separator film, and move in a direction of the first unit cell to horizontally bend the vertically bent surplus winding end portion in a direction of the upper surface of the first unit cell, so that the surplus winding end portion of the separator film is folded inward in the direction of covering the upper surface of the first unit cell, the first roller and the second roller allow the web to be interposed therebetween after the surplus winding end portion is horizontally bent, and then the first roller is moved downward and the second roller is moved upward, thereby performing a process of pressing the horizontally bent surplus winding end portion on the first unit cell; and the upper leg of the gripper fixes the first unit cell together with the horizontally bent surplus winding end portion of the separator film. (a) manufacturing a plurality of unit cells (121, 122, 123, 124) including a positive electrode, a negative electrode, and a separator, and arranging the unit cells (121, 122, 123, 124) on a separator film in a long sheet form to manufacture a web in which plate type unit cells are arranged on an upper surface of the separator film at predetermined intervals, so that the unit cells are sequentially stacked with the separator film interposed therebetween; (b) vertically bending a surplus winding end portion by moving upward a pair of rollers located on a boundary between the surplus winding end portion of the separator film, and a first unit cell of a winding start portion, which is arranged in a state of being spaced apart from a winding end portion of the separator film in the web, and moving the pair of rollers in a direction of the first unit cell to horizontally bend the surplus winding end portion, and said pair of rollers includes a first roller located at a relatively upper portion and a second roller located at a relatively lower portion in a process of horizontally bending the surplus winding end portion; (c) pressing the horizontally bent surplus winding end portion of the separator film on the first unit cell after interposing the web between the pair of rollers; and (d) winding by rotating a mandrel including one or more grippers composed of one or more upper legs configured to fix an upper surface portion of the first unit cell and one or more lower legs configured to fix a lower surface portion of the separator film corresponding to the upper legs so that the unit cells (121, 122, 123, 124) are sequentially stacked with the separator film interposed therebetween,