To provide a building estimation arbitration network system using the Internet in which a building planner goes into a homepage operated by an intermediary trader, can calculate detailed building design and a building cost price, also selects a plurality of provided house builders and can anonymously obtain the designs of the house builders and building cost estimation and can construct with design/building cost of higher satisfaction.

The server computer system 1 of the intermediary trader, the Internet personal computer 3 of the building planner and the computer system 5 of the house builder are connected by the Internet 2, and the server computer system has a general floor plan design planning part anonymously performing general calculation, a contact address input and access information issuing part calculating detailed design with secrecy obligation agreement, a design cost calculation notifying part, a house builder information providing part, a house builder estimation client inputting part, a house builder estimation applying part, a house builder estimation record notifying part and a house builder negotiation notifying part.