PURPOSE : A method for processing guarantee of a payment tool is provided to enable a customer to receive various kinds of incentives such as increasing a credit limit by securing all or a part of financial assets of the customer based on financial asset information stored in a storage medium.CONSTITUTION : Financial asset information of a customer is stored to a storage medium by linking with customer payment tool information. The financial asset information stored in the storage medium is checked when the customer uses a payment tool(215). A credit limit of the payment tool is adjusted or an approval for using the payment tool is processed based on a guarantee tool by setting all or a part of financial assets of the customer as the guarantee tool based on the checked financial asset information(240). The financial asset information includes more than one of balance information, real estate/estate information, and stock or bond information of the customer.? KIPO 2008