A multifunction peripheral stores normal user information for executing user authentication in and an auxiliary storage. The multifunction peripheral has a quick login mode for simple authentication. When registering a new user in the quick login mode, the CPU determines whether a login name in the normal user information of an existing user matches a login name of the new user. When the two login names match, the user is allowed to select whether to associate the new user with the existing user. When selected to associate the new user with the existing user, the quick user information of the new user including the first management information and the second management information is generated using at least user ID in the normal user information of the existing user, the first management information is stored in the auxiliary storage, and the second management information is stored in a main storage.