Positioning of a printing plate in an image recorder is performed by the same method used for punching positioning holes for printing press in the printing plate. Specifically, the positioning for image recording is performed with reference to an edge of the printing plate on the same side as the edge of the printing plate used as a reference for punching the positioning holes for printing press. When the positioning for punching the positioning holes for printing press is performed with reference to the central position of the printing plate, the central position of the printing plate is detected based on a measured width of the printing plate, and the positioning for image recording is carried out with reference to the central position. Consequently, an image recorded on the printing plate by the image recorder and the positioning holes for printing press in the printing plate always have the same positional relationship.