PURPOSE: To prevent editing errors due to manual operation by reducing the burden of an user.

CONSTITUTION: A document processing part 3 successively processes document data while storing the current numbers of volumes and pages in a current volume storage part 9 and a current page storage part 10. Then, when a part to be made into the grocery or the index is present, the operation for storing the numbers of the volumes and the pages of the part in an output data storage part 11 is continued until the document data is completed and the contents stored in the output data storage part 11 at last are outputted to a document output device 2. Thus, the grocery and the index for not only the single volume document but also the document over the plural volumes can be automatically prepared.