PURPOSE: To perform divided plate processing easily by a method wherein a plurality of files for printing are prepared based on each of a plurality of data for divided plate, and a plurality of divided plates are prepared by printing based thereon.

CONSTITUTION: An input unit inputs a copy data and an allocated data to a CPU 25. Further, input is performed to calibrate those characters or the like. A magnetic disk 24 holds readable and rewritable files of the allocated data, the copy data, etc., as an external memory of the CPU 25. The allocated data and the copy data are held on a magnetic tape 21 and are inputted to the CPU 25 therefrom. Then, a TCL composition process for dividing plate is performed and one plate composing data is prepared. At that time, a data from a plate dividing command data is inputted to the CPU 25 by a plate dividing indication input and plate dividing is performed based in this data. That is, two plate dividing data (magnetic tape) are formed, and each is printing processed by digital set. Thereby, a first plate (color plate) and a second plate (black plate) are prepared.