Printing plate forming method and cylindrical forming apparatus for printing plate

A method of forming a printing plate to be mounted on an outer periphery of a cylindrical plate cylinder, the method comprising:

• a notch forming step of forming a positioning notch in a rectangular elastic material sheet having a resin layer serving as a plate section formed on one surface of the elastic material sheet;
• a cylindrical material forming step of rolling the elastic material sheet in which the positioning notch is formed with the positioning notch configured to engage with a positioning stepped portion extending from an end stopper of a cylinder member having the same shape as the plate cylinder and joining both end portions of the elastic material sheet in an overlapped state to form a cylindrical shape;
• and
• a plate section engraving step of engraving a printing pattern at the plate section of the elastic material sheet formed into a cylinder shape by mounting the elastic material sheet on the plate cylinder.