A user detecting unit detects a mobile identification device in a communicable range of a wireless communication device, and determines a user in association with the detected mobile identification device and determines user authority of the user among general user authority and administrator user authority. The general user authority is prohibited from using a specific function allowed to the administrator user authority. The login processing unit performs a login process based on the detected user authority for the user. If the mobile identification device with the administrator user authority is detected after the login process based on the general user authority and a distance is less than a predetermined value between the detected mobile identification devices with the general user authority and the administrator user authority, then the authority changing unit changes the user authority of the user from the general user authority to the administrator user authority.