PROBLEM TO BE SOLVED : To prevent a breach of contract by enabling the prior recognition of the past breach-of-contract history of the renter or purchaser of a real estate and to prevent an illicit action related to a real estate business by enabling the prior recognition of the past illicitness history related to real estate business of a real estate company employee.SOLUTION : In a server 13 performing communication with each personal computer 11a-11n through a communication network 12, real estate credit information including predetermined personal information of an individual who performs a business for mediating the lease and trade of the real estate and information showing the content of the illicit action or damage related to real estate business of the individual is registered in a database. When a retrieval request using the personal information is received, in the server 13, the personal information is retrieved from registered information by a retrieval control part 26, and the real estate credit information including the personal information, in the detection of the personal information, or non-detection information, in no detection thereof, is reported to the personal computer 11b that is the retrieval requester.