A plurality of rough three-dimensional structured data, each expressing a shape of an object in a polygon pillar, are displayed on a display unit; one rough three-dimensional structured data is selected from the plurality of rough three-dimensional structured data displayed on the display unit in accordance with a request given by an input device; a detailed three-dimensional structured data corresponding to the selected rough three-dimensional structured data is retrieved from a set of detailed three-dimensional structured data which are stored in a storage unit and each of which expresses a shape of an object in detail; and the selected rough three-dimensional structured data is replaced by the corresponding detailed three-dimensional structured data.