PROBLEM TO BE SOLVED : To provide an environment, in which respective mediating companies can simultaneously develop business selling activities while keeping the consistency of transactions by introducing a common ID capable of dealing with each of mediated real estate property as unique one.SOLUTION : A unique code common for a real estate mediator 3 including an owner 4 having a contract determination right and a client 1 is applied to each of property published on a real estate mediation property information magazine, and the condition of making a contract is confirmed in real time by disclosing a real estate mediation property information database constructed on the basis of the relevant code through the WEB. Besides, meaning is applied to each of common unique codes and handled after being converted inside a computer. Thus, operability is improved and a security function is fulfilled.