PROBLEM TO BE SOLVED : To provide a real estate transaction support system capable of creating an estimate when simultaneously selling and purchasing a real estate. SOLUTION : The real estate transaction support system includes database having real estate information stored therein, an arithmetic processing unit, input means, and an output unit. The arithmetic processing unit includes : zoning means for zoning a site of a building into a zone planned to sell and a zone planned to possess according to an input of the input means; renovation/reconstruction setting means for setting a renovation or a reconstruction according to the input of the input means; and estimate calculation means for calculating a balance amount between an estimated land sale value of the zone planned to sell and a cost for the renovation or reconstruction of the building on the basis of the input content and displaying it onto the output unit. COPYRIGHT : (C)2013, JPO&INPIT