PROBLEM TO BE SOLVED : To provide a trading system device for real estate agency using a computer system allowing a seller and a buyer to directly register real estate information and to select and designate an agent from previously registered agents for mediating real estate trade between a borrower and the buyer for solving problems in a conventional real estate bulletin information system using the Internet intended for a real estate registered agent and a real estate company and for trading between a lender and the seller through the real estate registered agent or the real estate company and offering no desired information to the seller, the lender, the buyer, and the borrower.SOLUTION : In this computer system, a real estate information advertisement fee can be collected according to an advertisement available term, and consequently, a real estate information fee can be charged not only to the agency but also to the seller and the lender, so that a real estate agency fee can be discounted.