To ensure the properly tight attachment of a printing plate to a plate cylinder and also the easy attachment of the printing plate to and the easy detachment of the plate from the plate cylinder, with regard to the printing plate clamping device of the printer.

A printing plate clamping shaft 8 is fitted into a shaft fitting hole 7 at the innermost part of a groove 9 formed on the outer peripheral face of the plate cylinder 6 and a plurality of protrusions 5 for engaging the printing plate 1 are projectingly disposed on the printing plate clamping shaft 8. Further, a trailing 26 formed by bending at an obtuse angle close to a right angle through a fold, at the rear end part of the printing plate 1 mounted on the outer periphery of the plate cylinder 6, is inserted into the groove 9. Then, the protrusions 5 for engaging the printing plate 1 are inserted into a plurality of holes 2 for engagement formed in the trailing part 26. In addition, a bent part or a curved part 30 is provided at the trailing pat 26 so that the trailing part 26 is arranged so as to realize the further displacement of the tip 26a to the inside in the bending direction.