PURPOSE: To separate and designate an optional area, and to display a rule and a separating mark simultaneously, by displaying the separating mark on a display screen in accordance with positional information of the separate area which are stored in a document memory.

CONSTITUTION: Address data of a separated area are stored in an area table 10, and address data except the lift upper end and the right lower end of the area are calculated in a position calculating circuit 9 and are written. In the area separating processing, a discriminating circuit 5 compares the read address of a document memory 7 with contents of the area table 10 to discriminate whether the read adderss is the end address of the area or not and outputs the result to a code generating circuit 6. The code generating circuit 6 generates codes of the upper end, the left end, the right end, and the lower end and writes them in the document memory 7. Stored data in the document memory 7 are sent to a character generator through a display controller 12.