PROBLEM TO BE SOLVED : To provide a new index representing profitability of real estate for investment.SOLUTION : A computer calculates total rentable area of a property during a settlement term on the basis of property information and increase/decrease floor information, calculates a unit revenue a day by dividing a revenue at the settlement term by the total rentable area, compares the rentable area of the property on a day when an attention is paid (the day) with the rentable area of the property on the previous day among days included in the settlement term, calculates a smaller value as a rentable area common to the previous day, calculates a day-to-day increase/decrease rate by dividing the revenue on the day obtained by multiplying the rentable area common to the previous day by the unit revenue of the day by the revenue on the previous day obtained by multiplying the rentable area common to the previous day by the unit revenue of the previous day, sequentially exponentiates the day-to-day increase/decrease rates from the first day included in a prescribed period, and thereby calculates a profit index of real estate investment trust of each day included in the prescribed period of the property.SELECTED DRAWING : Figure 1