PROBLEM TO BE SOLVED : To easily construct a database so as to share property information about real estate, etc., among a plurality of agents by using a general-purpose data format.SOLUTION : In this property information database system, common tag data which define the attribute of each item regarding property information are distributed to a plurality of real estate agents 4a, 4b or to Web sites 5a-5c, property information data produced in tag data format is acquired by an information server 2 through the Internet from either of real estate agent 4a or 4b or from Web servers 5a-5c, and, on the basis of the tag data, the property information is organized and integrated so as to construct a property information database 21.