A device (1) for manufacturing a three-dimensional object by a layer-wise solidification of a building material at positions in the respective layers corresponding to the object is provided. The device has an energy source (6) that emits a beam (9) for solidifying the building material, a scanner (8) that selectively directs the beam (9) to different positions in a building plane (11), and a deflection mirror (7) that deflects the beam (9) coming from the energy source (6) to the scanner (8). The beam (9) from the energy source (6) to the scanner (8) runs in a space (13, 14) secluded from the outside and an adjustment mechanism (16) for the alignment of the deflection mirror (7) is provided, which is adjustable from the outside of the secluded space (13, 14).