Surface form data as an object to which a grain is applied is inputted to a data input part. A plane polygon forming part projects a borderline of the surface form data on an x-y plane and changes the borderline to poly-lines to form a two-dimensional polygon mesh having the borderline as an outer edge. A three-dimensional polygon forming part connects together intersections of straight lines extending to a z-axis direction from apexes of the polygon mesh and the original surface form data to obtain a three-dimensional polygon mesh and further make the mesh uniform. A grain forming part obtains an amount of displacement from texture data corresponding to the apex of the three-dimensional polygon mesh through a texture model formed and deformed in a texture model deforming part to set polygon data obtained by connecting together the apexes respectively displaced in normal directions as the surface processed data.