In a method which is performed using a communication network and uses a derivative to reduce a money debt such as a housing loan debt, a loan debt, a nation/public/corporate bond debt, a lease debt, or a payment obligation including insurance benefits, a derivative corresponding to a period of the debt and a condition is set up by a bond, a stock, a currency, an exchange, an interest rate, a spot such as a commodity and/or an index, and a price singly or by combining them, and in case of necessity, the derivative is divided into small lots to conform to an amount of the debt and the condition, this is purchased by a debtor of the debt at a relatively small premium, and when the derivative produces a profit, this is sold to realize the profit, alternately, reference is made to a present value of the debt and when a profit is produced in the money debt, a swap is made to realize the profit, and the debt is reduced by the profit.