PURPOSE: To automate perfect printing by a method wherein printing is made on one side of paper fed from a paper supply part to a printing part in a single- side printing process, a paper discharge tray is moved to be opposed to a second paper supply part, and printing is made on the other side of the paper in a perfecting process.

CONSTITUTION: A plate making printer provided with a plate making part 2, a plate supply part 3, a plate discharge part 8, and a printing part 10 comprises a first paper supply part 4 for feeding unprinted paper 42 toward the printing part 10, a first paper discharge tray 61 on which paper 42f subjected to single-side printing is stacked, a second paper discharge tray 71 on which paper 42b subjected to perfecting is stacked, a second paper supply part 9 for feeding the paper 42f on the first paper discharge tray 61 toward the printing part 10 when the first paper discharge tray 61 movable by a paper discharge tray moving means is positioned on a second position P2, and a paper discharge feed device 50 shakable by a feed path change-over means between a first paper discharge position HP1 to the first paper discharge tray 61 and a second paper discharge position PH2 to the second paper discharge tray 71.