The present invention provides an electrode assembly comprising: a first electrode stacked body in which at least one electrode unit having a first area is stacked; a second electrode stacked body in which at least one electrode unit having a second area less than the first area is stacked; and a stepped portion in which the first electrode stacked body and the second electrode stacked body are stacked in a vertical direction with respect to a plane, and which has step due to an area difference between the first electrode stacked body and the second electrode stacked body. The electrode assembly is formed by winding the electrode units by a rectangular separation film having a length in a horizontal direction that is longer than a length in a vertical direction, wherein the rectangular separation film is wound so that at least a portion thereof covers the stepped portion of the electrode assembly, and the electrode assembly has the same shaped step as the step of the stepped portion.