PURPOSE: To prevent a part which is inhibited from being updated by mistake and make a part that an editor can edits clear when plural persons updates the same source program.

CONSTITUTION: When the source program is edited, an editor check means 13 checks a current editor and a text converting means 18 converts a text according to the check result when the text file is inputted. Consequently, the update-inhibited part is made clear and disabled to be edited at the time of editing operation and the part which can be updated is made clear and allowed to be edited. Further, a text converting means 19 converts the text even at the time of text file output according to the check result, so the update-inhibited and allowed parts can be changed according to the current editor.