PROBLEM TO BE SOLVED : To enable comparison of profitability between a case that only an owner makes an investment for a building for rent and a case that a larger building for rent is constructed by joint investment the owner invests the same amount of money by using a profit margin simulator of buildings for rent to simulate the profitability of the building for rent and a print.SOLUTION : A fact that the profitability for the owner is improved when apartments are managed by the joint investment by a land owner and a real estate agency for a fixed period is presented to the owner. In this simulation, building main body and installed facilities are specified, the owner basically bears the cost amount equivalent to the building main body and the real estate agency bears the cost amount equivalent to the facilities with a comparatively short depreciation period during the joint investment period. A rent according to investment ratio is paid to the owner during the joint investment period, the facilities are sold to the owner and management is transferred to individual management after an elapse of period by taking of legal durable years of the facilities into consideration. Simulation results are graphically shown on a chart and printed out.