Abstract: An additive manufacturing device for manufacturing a three-dimensional object by selective solidification of a building material layer by layer, including a process chamber having a chamber wall, wherein the chamber wall of the process chamber has at least one elongate opening. The device includes a cover device having a cover area for covering and/or shielding the at least one opening, the extent of the cover area being variable in the longitudinal direction of the opening, and the cover device includes a plurality of individual elements of similar type that are connected to one another in such a way that they are movable relative to one another in the longitudinal direction of the opening.