PURPOSE : A system for managing a real estate rental by applying an Internet billing system is provided to minimize losses of a lessor and a hirer by applying an Internet billing system to a real estate rental, extending a rental contract by on-line, and calculating/charging/paying a rental charge by one day.CONSTITUTION : A demand institution inputs contract registration information of a user to an Internet billing server. The Internet billing server transmits a bill to a user computer through an E-mail by various kinds of demand details of the user inputted from the demand institution. The user checks the bill and requests a payment of a demand amount in an account through the Internet billing server. The Internet billing server receives the payment request of the user and requests a transfer approval of the demand amount from a payment account of the user to an account of the demand institution in an integrated financial institution server. The integrated financial institution server calculates payment amount, remits the payment amount to the account of the demand institution, and informs each payment approval result to the Internet billing server. The Internet billing server supplies a demand amount payment approval result to the user. The user becomes a hirer, and the demand institution becomes a lessor. If a real estate rental term is expired, the Internet billing server transmits a mail for asking a termination and extension intention of a rental term. If the hirer wants to conclude a contract again, the existing contract is extended through the Internet billing server or a contract is concluded as an adjusted condition.? KIPO 2004