1. A shape evaluation method for evaluating a curved surface of a shape by a characteristic line, wherein said characteristic line is a circular highlight line or a circular reflection line which an annular light source in an arbitrary direction in a three-dimensional space forms on said curved surface, said annular light source having a radius and a center that are variable, said characteristic line is formed by extracting points, where the light from said annular light source irradiates or reflects on said curved surface, from points on said curved surface by computing, and said computing obtains a vectorial correspondence between each of the points on said curved surface and positions on said annular light source.