1. A three-dimensional representation method for generating a three-dimensional image by displaying two-dimensional images on a plurality of image planes located at different depth positions, the method comprising the steps of: generating two-dimensional images in which an object to be presented is projected along the line of sight of an observer, onto a plurality of image planes located at different depth positions as seen from the observer; and changing brightness levels of the generated two-dimensional images individually for each image plane to display the generated two-dimensional images on the plurality of image planes.