PROBLEM TO BE SOLVED : To provide an online contract system transaction supporting system for real estate object, which can perform a series of procedures from the perusal of real estate information to a contract including a procedure for preferentially negotiating a specified object through the use of a communication network.SOLUTION : In the system 10, a real estate information service server 1 on which real estate object information is inserted is installed on the communication network and the transaction of the desired object can be supported from a communication terminal unit 2 connected on the communication network. The service server 1 preserves a temporary contract page 34 specifying the real estate object which a user desires. When the communication terminal unit 2 of a user side fills user recognition information and selection information specifying the real estate object which the user desires in the temporary contract page 34 and transmission is operated, temporary holding is registered in a user data base 4. Display that the real estate object is in the middle of temporary holding negotiation is added to the real estate object whose temporary holding is registered.