A method of synthesizing a real image and a computer graphic (CG) having a complex shape in which the normal vector of each of two adjacent planes of a rectangular parallelepiped CG circumscribed about the CG having a complex shape is determined from the coordinates of six vertices representing the two planes on the basis of a real image of a rectangular parallelepiped, and parameters for three-dimensional rotational transformation of the rectangular parallelepiped CG required for synthesis are determined on the basis of the normal vectors. A CG having a complex shape for synthesis is produced by rotational transformation thereof on the basis of the parameters, and the CG having a complex shape thus produced is synthesized on the real image.