A control device that is mounted on a communication apparatus and that is adapted to control a plurality of functions of the communication apparatus, comprising: an authentication means adapted to retain first authentication information and to authenticate, using the first authentication information, external devices (900-1 to n); an authenticated device counting means adapted to count a number of authenticated devices that were able to be authenticated by the authentication means, each authenticated device being an external device that exists around the communication apparatus and retains same authentication information as the first authentication information; an unauthenticated device counting means adapted to count a number of unauthenticated devices that were not able to be authenticated by the authentication means, each unauthenticated device being an external device that exists around the communication apparatus and retains authentication information other than the first authentication information; and a function controlling means adapted to restrict a first function and a second function of the functions when a first condition is satisfied, the first condition being determined by the number of the authenticated devices being less than the number of the unauthenticated devices or both of the number of the authenticated devices and the number of the unauthenticated devices being equal to zero, wherein the function control means is further adapted to restrict the second function rather than the first function when a second condition is satisfied, the second condition being determined by the number of the authenticated devices being greater than or equal to the number of the unauthenticated devices and the number of the unauthenticated devices being non zero. an authentication means adapted to retain first authentication information and to authenticate, using the first authentication information, external devices (900-1 to n); an authenticated device counting means adapted to count a number of authenticated devices that were able to be authenticated by the authentication means, each authenticated device being an external device that exists around the communication apparatus and retains same authentication information as the first authentication information; an unauthenticated device counting means adapted to count a number of unauthenticated devices that were not able to be authenticated by the authentication means, each unauthenticated device being an external device that exists around the communication apparatus and retains authentication information other than the first authentication information; and a function controlling means adapted to restrict a first function and a second function of the functions when a first condition is satisfied, the first condition being determined by the number of the authenticated devices being less than the number of the unauthenticated devices or both of the number of the authenticated devices and the number of the unauthenticated devices being equal to zero, wherein the function control means is further adapted to restrict the second function rather than the first function when a second condition is satisfied, the second condition being determined by the number of the authenticated devices being greater than or equal to the number of the unauthenticated devices and the number of the unauthenticated devices being non zero.