To provide a printing plate mounting method capable of certainly and easily mounting a flexible printing plate on a plate cylinder and restricting the elongation of the printing plate to 100 μm or less.

This mounting apparatus for the flexible printing plate is equipped with a printing plate pressing mechanism 17 for bringing the notch provided to the leading end of the flexible printing plate 70 into contact with the positioning pin 14 of a plate leading end clamping mechanism 12 to fix and press the same, a plate rear end fixing mechanism 13 and a block copy sheet 27 wound around the plate cylinder to be fixed thereto. The block copy sheet 27 is obtained by providing an uneven shape to at least the single surface of a support of which the initial elastic modulus is not less than 350 kgf/mm2 (350×9.8×106 Pa). The uneven shape comprises an uneven surface, which comprises particles with a particle size of 1-100 μm and binder resin, and the overcoat layer provided thereon.