PROBLEM TO BE SOLVED : To provide the more accurate timing signal of purchase and sale even in the case that there is the possibility that the timing of the purchase and the sale is lost by conventional investment judgment based on the profitability of a single period. SOLUTION : For the characteristics of real estate investment, the directivity of the change of average profitability in the case of continuous possession for a certain long period of time is stabilized. Thus, the purchase and sale timing signal of the real estate investment by which the tendency of the change of the profitability of real estate in the future can be recognized even while being based on data in the past is provided by using the average profitability in the case of the possession for a fixed period.