PURPOSE: To select an optimal center part for displaying character string, etc., in the graphic area inside without necessitating a correcting operation by an operator.

CONSTITUTION: This method is provided with a first step for generating a quadrangle circumscribed to an object graphic, and deriving an intermediate coordinate value of each side of this quadrangle, a second step for deriving an intersection of a first straight line being parallel to an X axis and a second straight line being parallel to a Y axis for passing through the intermediate coordinate value and a graphic, a third step for deriving a middle point of the intersection of a first straight line and a middle point of the intersection on a second straight line, a fourth step for generating a third straight line being parallel to the X axis or a fourth straight line being parallel to the Y axis for passing through the derived middle point, and deriving an intersection of a third straight line or a fourth straight line and the graphic, and a fifth step for selecting that which becomes the longest in distances between the intersections on the straight lines derived up to the present, and selecting the middle point between its selected intersections as a center part of the graphic area inside.