To improve the operability of a device at the time of performing processings such us preparing a suffix document, inserting it to a main document and outputting it.

When the suffix document is specified, a control part 5 stores a prepared document in a suffix document storage part 31 as the suffix document. Then, an insertion page input device 7 displays information for specifying the main body document and a message for inquiring to which page of the main body document the suffix document is to be inserted at a CRT 10. Thus, since the information for specifying the main body document and insertion page information are inputted as suffix insertion information to the control part 5, the header part of the specified main document is read from an external storage device 11 to a main document storage part 32, the suffix insertion information is written in the header part and it is returned to the external storage device 11. Thereafter, suffix information required for insertion to the main body document is written in a document header part on the suffix document storage part 31 and it is stored in the external storage device 11 as a different document.