Plate cylinder and plate mounting device

A plate cylinder comprising:

• a cylindrical plate-mounting surface on which a cylindrical printing plate is capable of being fitted from a front end side and mounted,
• a plate fixing member mounting surface having a flat surface arranged on an outer circumferential surface of the plate cylinder and bordered by the cylindrical plate-mounting surface, and
• a front stopper provided at an end portion of the front end side, wherein the front stopper includes a stopper main body and an operation permissible hole,
• wherein the front stopper is configured using the operation permissible hole to regulate a rotation of the stopper main body to switch the front stopper between a protruding orientation in which at least a portion of the stopper is positioned so as to protrude to an outside of the plate fixing member mounting surface in a radial direction and to come into contact with a circular plane surface end portion of the fitted cylindrical printing plate, and
• a retracted orientation in which an entire stopper is positioned to an inside of the plate fixing member mounting surface in the radial direction.