Terminal to register the address information of the user, method and program

The transferring unit transfers a message received from a PC or a network to a designated destination address. The judging unit judges whether an authentication message including the identification information of the user and a grant message indicating that the user is authenticated are transferred. The identification information acquiring unit acquires the identification information from the transferred authentication message. The SIP message processing unit creates a registration message that includes the address information of the user having the acquired identification information and transmits the created registration message to the SIP server when the grant message is transferred.