To detect the optimal realistic construction cost by unitarily managing processes from the design stage of a construction to the procurement of building materials.

An application service provider(ASP) comprises a construction design system consisting of a three-dimensional (3D) structure design system for designing a construction as a 3D structure by means of a 3D CAD means and a direct building construction cost calculating means for calculating the building materials and amounts of the construction for each building material by means of the design system, comparing them with stared general data and calculating the optimal direct construction building cost, and a total construction information system for comparing the design data of the construction designed by the construction design system with latest construction building materials data, talent information data and logistic information data or the like acquired from an Internet service provider(ISP) and detecting the optimal realistic contraction cost.