1. A method for generating an orthophoto image comprising: divisionally-capturing a target region from a platform such as an airplane by rendering viewing angles as being different from each other as well as rendering a focal length as being different with reference to a predetermined ground resolution; thereafter generating an elevation model of an entire target region in accordance with matching of elevation models generated based on respective divisionally-captured images among image capturing overlap regions; and generating an orthophoto image of the entire target region by applying an orthogonal projection transformation processing to the respective divisionally-captured images by use of altitude information of the elevation model.