An orthographic projection creating unit creates an orthographic projection image from an optical image of an ground surface acquired by an optical camera, and a DSM generating unit generates a DSM from the orthographic projection image. A laser point group data generating unit generates three-dimensional point group data based on a laser measurement result of the ground surface by a laser measuring device. An object generating unit groups altitude data of the DSM and altitude data of the three-dimensional point group data for each of objects such as buildings. A synthesizing unit extracts the same objects from the grouped altitude data of the DSM and three-dimensional point group data, associates the objects with each other based on respective coordinate information thereof, and replaces altitude information of the optical image by high-accuracy altitude information of the three-dimensional point group data for each of the objects.