1. An apparatus for constructing three-dimensional surface shading image display from three-dimensional sequential tomographic images, comprising: individual distance image constructing means for constructing an individual distance image for each of the tomographic images with respect to a predetermined reference plane; synthesized distance image constructing means for constructing a synthesized distance image in which the individual distance images for all of the tomographic images constructed by the individual distance image constructing means are synthesized together, by sequentially carrying out an image extrema calculation between each m-th individual distance image for each m-th tomographic image and a previous synthesized distance image in which the previous individual distance images for up to (m-1)-th tomographic image are synthesized together, where m is an integer and the image extrema calculation calculates an extremum value for each picture element in the individual distance images; surface shading distance image constructing means for constructing a distance image for surface shading in a predetermined shape by applying an affine transformation to the synthesized distance image constructed by the synthesized distance image constructing means; and shading process means for obtaining a surface shading image by applying a shading process to the distance image for surface shading constructed by the surface shading distance image constructing means.