PURPOSE: To remarkably shorten the preparation time for printing while maintaining the positioning accuracy of an original plate by using positioning pins and holes corresponding to the pins between processes such as plate making, press plate making and printing.

CONSTITUTION: Register marks 3 are formed on an original plate (key sheet) 2, and holes 4aW4d for positioning pins used to patch up a halftone original plate and holes 5a, 5b for positioning pins for exposure are cut in the plate 2. The holes 5a, 5b are set to positioning pins 7a, 7b attached to the exposing head 8 of an automatically exposing machine 10. An offset printing plate 12 is mounted on the exposing table 11, and holes 16, 17 cut in the plate 12 are set to positioning pins 14, 15 so attached to the table 11 that they can be put in the table 11. Holes 19W21 corresponding to positioning pins attached to a plate cylinder are cut in the plate 12 at 3 positions. Thus, by making use of pins and holes for the pins between processes the registering accuracy of the original plate 2 is maintained easily, and the preparation time can be shortened remarkably.