To provide a printing plate mounting method in a printing press which enables the accurate and stable mounting of a planographic printing plate, especially a flexible printing plate, which has paper, a plastic resin film or a composite material of them as a support, when the flexible printing plate is mounted on the surface of a plate cylinder through a substrate plate, excellent in the register accuracy of repeated plate replacement and enabling printing not inferior to a PS plate.

In the printing plate mounting method in the printing press, a block copy double-side pressure-sensitive adhesive sheet preliminarily subjected to uneven processing is bonded to the substrate plate when the flexible printing plate is mounted on the surface of the plate cylinder through the substrate plate and the flexible printing plate is mounted on the pressure-sensitive adhesive sheet to be fixed thereto.