A communication management system comprising: a terminal of a user; an authentication server operable to authenticate the terminal; and a management server which is provided separately from the authentication server and which is operable to manage an IP address which uniquely identifies the terminal on a network, the terminal comprising: a holding unit for holding a device ID which is fixedly assigned to the terminal and which uniquely identifies the terminal; an authentication request unit for reading the device ID from the holding unit, and for sending the device ID to the authentication server so as to make a request for authentication; a certificate acquisition unit which is operable to acquire a certificate, which certificate certifies success in the authentication of the device ID, from the authentication server; and a registration request unit operable to send the certificate to the management server, so as to make a request for registration of the IP address, which is assigned to that terminal, the authentication server comprising: an authentication reception unit operable to acquire the device ID from the terminal and to receive the request for the authentication; a terminal database for holding a device ID unique to the terminal to be authenticated; an authentication unit for authenticating the correctness of the device ID of the terminal by referring to the terminal database; a ticket issue unit which is operable to issue a certificate when succeeding in the authentication of the terminal; and for issuing a locator ID for uniquely identifying the terminal when succeeding in authentication of the terminal; and a communication control unit operable to transmit the certificate issued by the ticket issue unit and the locator ID issued by the ticket issue unit to the terminal; the management server comprising: a database for holding the locator ID issued by the ticket issue unit, and the IP address in a manner that they are associated with each other; a registration reception unit operable to acquire, from the terminal, the certificate, the locator ID issued to the terminal by the ticket issue unit, and the IP address of the terminal, and to receive the request for registration of the IP address of the terminal; a registration unit operable to verify the correctness of the certificate, and to register the locator ID and the IP address of the terminal in the database when the certificate is confirmed to be correct; an inquiry reception unit for receiving a request for inquiring the IP address of the terminal; a search unit for searching through the database on the basis of the locator ID of the terminal as the target of an inquiry, to acquire the IP address of the terminal; and an answer unit for returning the IP address of the terminal acquired by said search unit. a terminal of a user; an authentication server operable to authenticate the terminal; and a management server which is provided separately from the authentication server and which is operable to manage an IP address which uniquely identifies the terminal on a network, a holding unit for holding a device ID which is fixedly assigned to the terminal and which uniquely identifies the terminal; an authentication request unit for reading the device ID from the holding unit, and for sending the device ID to the authentication server so as to make a request for authentication; a certificate acquisition unit which is operable to acquire a certificate, which certificate certifies success in the authentication of the device ID, from the authentication server; and a registration request unit operable to send the certificate to the management server, so as to make a request for registration of the IP address, which is assigned to that terminal, an authentication reception unit operable to acquire the device ID from the terminal and to receive the request for the authentication; a terminal database for holding a device ID unique to the terminal to be authenticated; an authentication unit for authenticating the correctness of the device ID of the terminal by referring to the terminal database; a ticket issue unit which is operable to issue a certificate when succeeding in the authentication of the terminal; and for issuing a locator ID for uniquely identifying the terminal when succeeding in authentication of the terminal; and a communication control unit operable to transmit the certificate issued by the ticket issue unit and the locator ID issued by the ticket issue unit to the terminal; a database for holding the locator ID issued by the ticket issue unit, and the IP address in a manner that they are associated with each other; a registration reception unit operable to acquire, from the terminal, the certificate, the locator ID issued to the terminal by the ticket issue unit, and the IP address of the terminal, and to receive the request for registration of the IP address of the terminal; a registration unit operable to verify the correctness of the certificate, and to register the locator ID and the IP address of the terminal in the database when the certificate is confirmed to be correct; an inquiry reception unit for receiving a request for inquiring the IP address of the terminal; a search unit for searching through the database on the basis of the locator ID of the terminal as the target of an inquiry, to acquire the IP address of the terminal; and an answer unit for returning the IP address of the terminal acquired by said search unit.