An apparatus for controlling the temperature of a recording material, in particular a printing plate, in an exposer for recording printing originals. An exposer has an exposure drum for holding the printing plate, and has a cylinder. An internal pipe and webs connect the cylinder to the internal pipe. Using a rotary lead-through, a temperature-control liquid is led into the internal tube of the exposure drum and, by thermal conduction via the webs and the cylinder, keeps the printing plate at a constant temperature.