PROBLEM TO BE SOLVED : To provide a method and a system for electronic real estate transaction to which conditions advantageous for a seller can be introduced with the procurement of funds without requiring costs required for moving a house or store and further without finally losing owned real estate by enabling the continuous use of the real estate even after selling of owned real estate.SOLUTION : The auction is held for making bids while presenting a purchase factor determined on the basis of predetermined conditions for the seller of real estate to buy real estate back from a buyer at the time point of lease period fulfilling while leasing the real estate from the buyer with a fixed period after selling of real estate to the buyer, and a successful bidder is determined on the basis of a deciding method with this purchase factor as an element.