According to the present invention, number 1 and number 2 client computers disk-plurality of including at least one server network connecting with each other by way real estate rental agency management system, said server is performed by rental agency contract it is intended to provide a method. The of the present invention method, said number 1 client computer from the steps of receiving conditions contract number 1, number 2 contract conditions said number 2 client computer from the steps of receiving, at least one of the number 1 and number 2 contract conditions said number 1 and number 2 contract conditions coincide step for judging whether or not a mobile, said discriminating step said number 1 and number 2 contract condition is determined not coincident with when, said number 1 and number 2 contract is adjusted on the basis of the conditions creating a contract conditions, said adjusted contract conditions generated said number 1 and number 2 client computer-, and said adjusted from both client computer said number 1 and number 2 contract conditions for the agree upon receipt of the message, said adjusted contract conditions determines that are satisfied while a contract includes.