Before obtaining service from an installed terminal, a mobile unit can be authenticated (subauthenticated) only by the operation of the mobile unit such as an unauthenticated digital camera, etc. using an authenticated mobile phone. A digital camera is radio-connected with an installed terminal, and the digital camera is also radio-connected with a mobile phone of a user. The installed terminal center is notified of the identification code of the mobile phone through the digital camera and the installed terminal. The installed terminal center inquires of the carrier center about the validity/invalidity of the mobile phone. Upon receipt of the notification of the validity of the mobile phone from the carrier center, the installed terminal center permits service to the installed terminal in the installed terminal.