Abstract: The irradiation apparatus for the photopolymerization of plastic embedding masses for histological preparations has a preparation support located in a housing and a plurality of irradiation lamps, with one lamp above and one lamp below the preparation support forming one lamp pair. In order to cure photopolymerizable embedding masses in a manner that does not harm the embedded preparations or specimens, and in particular to avoid an abrupt rise in the reaction heat, and so that a small number of irradiation lamps is sufficient, the preparation support is a rotary support plate having a plurality of light pervious preparation holding means located about its outer circumference, and the lamps are positioned such that in operation, the holding means sequentially pass in between the lamps of each lamp pair, and the centers of the holding means are located on a circle that is concentric with the axis of rotation of the support plate.