A device (48) for calibrating an irradiation system (18) of an apparatus (10) for producing a three-dimensional work piece comprises a control unit (50) adapted to control the irradiation system (18) so as to irradiate a radiation beam (22; 22a, 22b) onto an irradiation plane (52) according to a calibration pattern. The device (48) further comprises a sensor arrangement (56) adapted to be arranged in the irradiation plane (52) and to output signals to the control unit (50) in response to being irradiated with the radiation beam (22; 22a, 22b) according to the calibration pattern. The control unit (50) further is adapted to generate a digital image of an actual irradiation pattern produced by the radiation beans (22; 22a, 22b) incident on the sensor arrangement (56) based on the signals output by the sensor arrangement (56), to compare the digital image of the actual irradiation pattern with a digital image of a reference pattern so as to determine a deviation between the actual irradiation pattern and the reference pattern, and to calibrate the irradiation system (18) based on the determined deviation between the actual irradiation pattern and the reference pattern.