A building container (25) for a device (1) for manufacturing a three-dimensional object by a layer wise solidification of a building material in powder form at positions in the respective layers that correspond to the object is provided. A support device (26) is provided that is arranged in the building container (25) such that it is vertically movable, wherein the support device (26) has an upper side that forms a building platform (78), on which the three-dimensional object is generated layer wise. Between a circumferential outer edge of the building platform (78) and a circumferential inside wall (79) of the building container (25) a gap (80) is formed and a seal (81) is provided that is provided circumferentially at the building platform (78) and closes the gap (80). The seal is made from a ring of a flat flexible material having an outer diameter, which in a flat state is larger than the inner diameter of the inside wall (79). A guide plate (82) is provided that maintains the seal (81) in the region of the gap (80) in an angulated shape.