Abstract: Designing of building structures, reexamining designs of the building structures and processing of building structural components of the building structures are integrally conducted based on CAD data formed with a CAD device. A cost estimation table is constructed based on data formed with a CAD program. Furthermore, a strength distribution diagram of selected building structural components, which are selected from a virtual three dimensional model constructed with the CAD program, is formed. Upon examining the cost estimation table and the strength distribution diagram, if the design of the building structure is satisfactory, the structural components are processed with a CAM device.