An external cover of a user device includes: an upper cover; a lower cover; and a hinge connecting the upper and lower covers for pivoting the upper cover and lower cover over a front surface and a rear surface of the user device, wherein the upper cover opens and closes a front surface of the user device and comprises at least two or more folding lines along a longitudinal direction of the upper cover such that the upper cover is divided into at least three supports when folded along each of the at least two or more folding lines, and wherein the lower cover holds the user device on an inside surface, and slip preventing units are provided on at least two end surfaces of an outside surface of the second cover for providing enhanced friction between the second cover and a flat location so that the lower cover maintains a stable state in various holding mode of the lower cover facing the hinge, respectively, so that the lower cover maintains a holding state in various holding modes.