shows a somewhat differently constructed embodiment in an operating phase before the positioning pin 3 or 3 39 engages in the recess 5 and the positioning pin 4 or 4 39 in the recess 6 a round shape but flattened at the front was selected for the positioning pin 4 or 4 39 in this illustration so that a positioning pin 4 or 4 39 in the recess 5 could not make any contact the sensors could of course also be formed in a different way as already indicated hereinabove it is essential in this regard that an indication be given only when the printing plate 1 is inserted laterally correctly and the positioning pins 3 and 4 or 3 39 and 4 39 come to bear entirely in the recesses 5 and 6 fig2 shows an embodiment with a plate feeding device 13 which serves for making ready a printing plate 1 to be fed to the leading edge clamping device 14 of a plate cylinder 2 in an embodiment of this type a printing plate 1 is introduced from above into the non illustrated end of the plate feeding device 13 until the positioning pins 3 and 4 of the plate feeding device 13 engage in the recesses 5 and 6 on the printing plate leading edge 7 the positioning pins 3 and 4 are arranged on the lower end of the plate feeding device 13 and are displaceable in the direction of the double headed arrows 22 for engagement in the recesses 5 and 6 which cannot.