To provide a printing plate positioning device which precisely guides a printing plate and does not deform the groove part of the printing plate.

This printing plate positioning device comprises a printing plate guide table 5 which is obliquely held toward a vise 18 on the biting side of a plate cylinder 16 and has a suction means installed, in a freely movable manner, in the oblique direction, a table positioning pin 16 which is provided protruding on the vise 18 of the biting side of the plate cylinder 16 and engaged with the lower end of the plate guide table 5 and a printing plate positioning pin 17 which is provided protruding on the vise 18 on the biting side of the plate cylinder 15 and engaged with a printing plate positioning groove formed in a printing plate 12. In addition, the device is of such a construction that a guide 9 having a guide groove is installed at the lower end of the printing plate guide table 5 and cancels an operation to suck and hold the printing plate 12 and allows the plate 12 to slide down by only a microgap, when or before the guide groove comes into contact with the table positioning pin 16, and the printing late 12 comes into contact with the printing plate positioning pin 17 of the plate cylinder 15.