PURPOSE: To execute the writing processing at a high speed.

CONSTITUTION: In the graphic processing method for displaying an image by executing a graphic processing, based on apex data of a polygonal graphic, based on graphic data containing coordinates of two points on the graphic and a normalized normal vector, a coordinate calculating means 2 for deriving a coordinate of a point for interpolating between two points, a normal vector calculating means 3 for deriving a normal vector of an interpolated point, and a writing processing part 4 are provided, and the normal vector calculating means 3 is constituted so that an angle made by the normal vectors of two points is calculated, and also, its angle is divided, based on the number of divisions of two points, a normalized normal vector of an interpolated point is calculated based on the normal vectors of two points and the divided angle, and a writing processing is executed by the normalized normal vector and a vector required for the writing processing.