To equalize business investment and minimize cost.

A method for determining an investment upper limit includes the following processes: a process for calculating investment priority to present each class of equipment and effect of interannual business investment; a process for setting a life reaching year by following a predetermined life expectancy probability distribution of each retained equipment; a total cost calculation process for calculating total annual cost by summing an equipment update cost including depreciation cost of invested equipment while specifying invested equipment and equipment abandonment cost, a depreciation cost of the retained equipment other than the invested equipment, and a retention cost including regular maintenance cost and expeditious preservation cost; a gross cost calculation process for calculating gross cost by summing yearly total cost from an inaugural accounting year to a terminal accounting year; and a process for designating the investment upper limit which minimizes the gross cost as an optimum value by repeating the processes for calculating total cost and calculating gross cost while varying the investment upper limit.