PROBLEM TO BE SOLVED : To reduce an economic burden of a real estate dealer in a contract concluding system applied to leasing of real estate such as a warehouse, a shop (a restaurant, a bar, or a store) or the like.SOLUTION : An application for posting of unmodified real estate information is performed in a posting applicant client 3 side, and the unmodified real estate information is posted by an operator server 2 side by uploading it on a predetermined operated site. The operated site is accessed by a transaction applicant client 4 side and lease/buying negotiation desire information related to the unmodified real estate information is sent by the client 4 side. The lease/buying negotiation desire information is received by the posting applicant client 3 side. By this, a lease contract is concluded of the real estate in an unmodified state, and the real estate dealer can save costs required for disposing facilities added to the real estate or adding new facilities to the real estate.