PURPOSE : A surety insurance system for transaction of a real estate with a put-back option and a transaction system of real estate therein are provided to implement the real estate transactions through the put-back option having reliability in online thereby activating the real estate transaction. CONSTITUTION : A real estate display price searching unit(22) inquiries a market price of a real estate similar to a specific real estate from a real estate display price server(2). A real estate display price estimator(24) produces an estimated value of a transaction target real estate. An insurance policy database(31) stores real estate transaction history set put-back option and agreement subject of an insurance stock. An insurance policy expiration processor(32) processes expiration of the insurance stock through comparison between sale price and the appraisement.