PURPOSE: To improve operability of the device at the time of executing such processings as preparation of a suffix document, insertion into a main body document and output, etc.

CONSTITUTION: When A suffix document is designated, a control part 5 stores a prepared document in a suffix document store part 31 as a suffix document, Subsequently, an insert page input device 7 displays information for specifying a main body document, and a message for inquiring into which page of its main body document the suffix document is inserted, on a CRT 10. As a result, the information for specifying the main body document and the insert page information are inputted to the control part 5 as suffix insert information, therefore, from an external storage device 11, the header part of the specified main body document is read out to a main body document store part 32, and the suffix insert information is written in this header part, and returned to the external storage device 11. Thereafter, the suffix information required for insertion to the main body document is written the document header part on a suffix document store part 31, and it is stored in the external storage device 11 as a separate document.