PURPOSE: To ensure that a printing plate cylinder is initially set with accuracy and rapidity.

CONSTITUTION: A key hole 10 is provided, in a recessed fashion, on one lateral part of a printing plate cylinder 1, and a key 5 which engages with a key hole 10 is provided on the tip of a support shaft 2. In addition, a means 6 for detecting a phase which determines the positioning of the key 5 at a specified phase is installed on a frame 3 for supporting the support shaft 2 axially. Further, a drive mechanism for setting a phase is provided that rotates the support shaft 2 for setting the initial reference phase of the support shaft 2. The support shaft 2 is set to a reference phase based on the detection results of the means 6 for detecting a phase, in a state that the plate cylinder 1 before the start of printing is not held by the support shaft 2. At the same time, the plate cylinder held by a pair of support shafts 2 is set to a printing start phase by allowing the plate cylinder 1 to rotate by a specified intrinsic angle. These setting are achieved by a plate cylinder phase setting control device 7 which controls the drive of the drive mechanism for setting a phase.