According to the present invention, a polarized image is captured, a variation in its light intensity is approximated with a sinusoidal function, and then the object is spatially divided into a specular reflection area (S-area) and a diffuse reflection area (D-area) in Step S402 of dividing a reflection area. Information about the object's refractive index is entered in Step S405, thereby obtaining surface normals by mutually different techniques in Steps S406 and S407, respectively. Finally, in Steps S410 and S411, the two normals are matched to each other in the vicinity of the boundary between the S- and D-areas.