PURPOSE: To quickly execute the plotting of a screen by deciding a state of an overlap to a segment and registering its result in a segment management table, and determining the sequence of a display of the overlap segment.

CONSTITUTION: The device is provided with a segment management table 5 for holding a segment defined by a graphic defining part 1, or information related to a segment whose attribute is changed, and a result of decision by an overlap deciding part 3, the overlap deciding part 3 for referring to the segment management table 5, and also, deciding a state of an overlap between the segment, which follows a definition and an attribute change of a new segment, based thereon, and registering a result of decision in the segment management table, and a segment managing part 4 for determining the sequence between the segments having areas overlapping to each other. In such a way, the display which follows addition of the segment and an attribute change of the existing segment can be executed at a high speed.