In order to provide a rotary printing machine for direct printing, in which the printing-assembly cylinders are guided in a stable manner by means of a cost-effective device, the forme cylinder and the impression cylinder of a printing assembly are mounted, adjustably in terms of their mutual spacing, in side walls. At least one of the two cylinders is mounted on both sides in slides movable on straight guide elements which are arranged in each case on at least one of two opposite panels of an aperture in the side walls.