PURPOSE: To prevent the master paper from being damaged or stained by a method wherein the rear end of the master paper, in addition to the front end thereof, is retained on and released from a plate cylinder automatically in a master paper retaining device for which an automatic plate feeding and removing method is adopted.

CONSTITUTION: On the occasion of feeding of the master paper 8, the master paper 8 is sent automatically on to the peripheral surface of the plate cylinder 1, the front end thereof is touched on a catching part 1a and caught to be fitted by a catching pawl 13 by the operation of a front retaining member 12, while the rear end of the master paper 8 is positioned along the peripheral surface of the printing drum so as for it to touch a catching part 1b and then the rear end is caught to be fitted by a catching pawl 17 by the operation of a rear retaining member 16. On the occasion of removal of the master paper 8, the catching pawl 17 is released from the catching part 1b by the automatic operation of the rear retaining member 1b and thereby the retention of the rear end of the master paper 8. Next, catching pawl 13 is released from the catching part 1b by the operation of the front retaining member 12 and thereby the retention of the front end of the master paper 8 is released.