1. An automatic three-dimensional structure shape generation apparatus for automatically generating a shape of a three-dimensional structure from a plurality of points having three-dimensional coordinates containing height information, comprising: means for constituting a point group by collecting such points that three-dimensional distances between said points are within a predetermined threshold or two-dimensional distances and height differences between said points are within predetermined thresholds; means for detecting a polygon that includes the points of the point group at a minimum area from at least one of a plurality of predetermined polygons; and means for generating one of an outer shape and a rooftop shape of the three-dimensional structure based on said detected polygon having the minimum area.