PROBLEM TO BE SOLVED : To provide a system which conducts negotiation or contract of a newly-built object or a remodeled object, construction, temporary residence, moving, confirmation and meeting after move-in, and package sales, or the like.SOLUTION : This system prepares a WEB server, an object information database, a customer information database, a data transmitting means which transmits data between a customer' s terminal and a server system; a customer accesses the WEB server, refers information stored in the object information database and conducts negotiation, and the customer information is stored in the customer information database; when the contract comes up to a particular stage, a WEB page for each customer and a communication means using a data transmitting means such as mail address are set in the server system; and a process which transmits information including authentication information such as set mail account, URL of the WEB page, ID and password to the customer' s terminal, and a process which stores and accumulates contract information of the object data and others, construction information, move-in information, maintenance information, and other information of each customer in a memory area of each customer of the customer information database, are conducted.