PROBLEM TO BE SOLVED : To provide a real estate buying and selling supporting system capable of simplifying the buying or selling and lease of real estate, and efficiently executing transaction. SOLUTION : This real estate buying and selling supporting system is provided with a server (advertising agent) 12 for accepting the registration of the data of the non-contracted property of real estate, and for carrying the data on the web page of an Internet 11 so that the data can be read by a plurality of client terminals. In this case, the contact destination of a person who wants to buy or sell or lease the real estate is included in the data carried on the web page of the server 12 so that the person who tries to buy or sell the property or a lessor can contact the contact destination in order to directly negotiate with each other without asking any mediator for help. Therefore, it is possible for a client terminal 14 to read the web page, and it is possible for a person who wants to buy or sell his or her desired property to directly contact, and to freely negotiate with the other party who carries the data.