1. A rendering apparatus comprising: radiant-energy calculating means for determining a spectral radiance for each infinitesimal area of an object by using a spectral radiance of a light source irradiating the object, a spectral reflectance in the infinitesimal area of the object at a predetermined angular condition, and a three-dimensional spectral reflectance factor in a wide area of the object; color-specification-value calculating means for calculating color specification values of a colorimetric system on the basis of the spectral radiance obtained for said each infinitesimal area; transforming means for transforming the color specification values into image data for displaying an image of the object; and display means for displaying the image of the object on the basis of the image data.