PURPOSE: To produce the secondary documents like the footnotes, the captions, etc., in a small number of operations and without affecting the layout and the data of the documents by setting those secondary documents in terms of key words and holding the set secondary documents in a character string storage area together with the key words.

CONSTITUTION: An optional character string is set in response to a designated key word in the document data and stored in a character string storage area 114. A character string setting/editing means 104 edits the character strings which are set and stored in the area 114. Then a secondary document extracting means 105 extracts a secondary document right after the key word designated in the document data. Thus the secondary documents like the footnotes, the captions, etc., can be set in response to the key word designated in the document data. Then the footnotes and the captions are easily set in the document data by extracting the secondary document right after the designated key word included in the document data.