1. A three-dimensional terrain-information generating system for generating three-dimensional terrain information by mapping elevation-data including altitude information that is mapped onto a two-dimensional plane onto building/road map information and by removing effects of a building, comprising: a flow analyzer that extracts a flow portion from the elevation-data; a matching unit that receives the extracted flow portion and that matches coordinates of the elevation-data with coordinates on a building/road map; a reference region obtaining unit that obtains a reference region for creating three-dimensional terrain data from the elevation-data; and a surface fitting unit that performs the fitting of a surface so that the surface includes the reference region on a face thereof.