A security system to give a user in a specific area use authority based on authentication, and to permit use of the specific area by the use authority. The security system includes an authentication unit to authenticate a user, a position detection unit to detect at least one of a position and move of a user, and a use authority control unit to monitor at least one of a position and move of a user to whom the use authority is given based on the authentication of the authentication unit by a detection output of the position detection unit, and, if a distance between users is equal to or below a predetermined value, to change the use authority which is given to each user.