An apparatus for producing a three-dimensional work piece comprises a process chamber accommodating a carrier for receiving a raw material powder and an irradiation device for selectively irradiating electromagnetic or particle radiation onto the raw material powder applied onto the carrier in order to produce the work piece from said raw material powder by an additive layer construction method, the irradiation device comprising at least one radiation source and at least one optical unit with a plurality of optical elements. A heat transfer arrangement is configured to transfer heat generated by a heat source to the at least one optical unit of the irradiation device. The apparatus further comprises a control unit configured to control the heat transfer arrangement so as to adjust a temperature of the at least one optical unit of the irradiation device.