Apparatus for additively manufacturing three-dimensional objects

Apparatus (1) for additively manufacturing three-dimensional objects (2) by means of successive layerwise selective irradiation and consolidation of layers of a build material (3) which can be consolidated by means of an energy beam (5), which apparatus (1) comprises an irradiation device (6) adapted to guide an energy beam (5) across a build plane (4), characterized by a calibration device (7) comprising a positioning unit (8), a determination unit (9) and a calibration unit (10), preferably arranged in a process chamber of the apparatus (1), that is adapted to at least partially reflect the energy beam (5), wherein the irradiation device (6) is adapted to guide the energy beam (5) to the calibration unit (10) for generating a reflected part (12) of the energy beam (5), wherein the positioning unit (8) is adapted to position the irradiation device (6) dependent on at least one parameter of the reflected part (12) of the energy beam (5) determined via the determination unit (9).