The rendering parameters including the position coordinate, the color information and the transparency in a vector definition space are calculated for each pixel occupied by a curved surface model projected on a screen. Plural primitive data are generated and stored from the vector data. By judging whether the plural primitive data include the position coordinate or not, a rendering judgment variable is determined, and in the case where the rendering judgment variable is added an odd number of times, the raster data of the pixel corresponding to the position coordinate is generated based on the rendering parameters.