Abstract: A printing machine, especially an office offset printing machine, in which a master before being wrapped around the master cylinder is pre-curved by sliding over an edge of one pivotable part of a bipartite table which part is tilted manually during the mounting of the master to expose said edge against which the master is guided by a roller positioned above the table and by a guiding and operating member arranged between the two parts of the table. The curvature may be preadjusted in accordance with the characteristics of the master by adjusting the relative end positions of said roller and said table edge. The end of the movable table part closest to the master cylinder forms together with a guiding plate a slot which guides the master until it is gripped by the master cylinder. By actuating a handle and thereby raising one end of the movable table part the other end is lowered and thus said slot facing the master cylinder is opened to avoid straightening of the pre-curved master.