PURPOSE: To make it possible to edit an inserted document in which data is inserted in the same way as a normal document when a correction is required and to preserve the inserted document by displaying new document data on a display means before the new prepared document data is printed.

CONSTITUTION: In an insertion command 31, an insertion line number is 2 and an insertion column number is A. In the same way, the line number is 2 and the column number is B in a command 32, the line number 2 and the column number is C in a command 33, and the line number is 2 and the column number is D in a command 34. By the insertion data substitution processing program within a page, the command 31 is substituted for 2 lines and an A column. In the same way, the command 32 is substituted for 2 lines and a B column, the command 33 is substituted for 2 lines and a C column, and the command 34 is substituted for 2 lines and a D column and they are displayed on a CRT display part as shown the first time. Because 2 which is the same line number in all the commands is preserved as the preserved maximum line number, 3 is set as a start number by an insertion data substitution main processing program and the result of the second time is displayed on the display part by substituting the 2 lines for 3 lines. Thus, a user can confirm the results.