PROBLEM TO BE SOLVED : To provide a transaction method for used house by linking designated performance appraisal institution, plural real estate selling companies and a purchase applicant through the Internet.SOLUTION : Plural real estate selling companies 10, through the Internet 14, not only provide used house property information to the purchase applicant 18, but also transfer the used property information, from the real estate selling companies 10, to the designated performance appraisal institution 12, so that the designated performance appraisal institution 12 appraises the used house property information by a unified standard and provides the result through the Internet 14.