To secure the security of a computer system by providing the function of authenticating an alternative user, thus enabling a user with a different authority to alternatively perform operations for increasing operating efficiency and convenience, while identifying within the system the user who did the proxy operations and the user who made a request.

When an alternative user ID and an alternative user password are inputted from a login screen of a terminal device 2, a business system 100 requests the user ID and the password of the alternative user from the terminal device 2. Once the user ID and the password of the alternative user are inputted from the terminal device 2, the operations that the alternative user can alternatively perform are determined on the basis of the inputted user ID, password, alternative user ID, alternative user password, and the content of an alternative authentication information file 163 and the execution of the operations is permitted.