A communication terminal device performs communication based on a communication protocol defined so that first identification information assigned to the device is transmitted to and received from a communication party. The device includes an identification information generating section for detecting, based on information unique to the device, second identification information different from the first identification information, a storage section for storing a table representing a correspondence between the generated second identification information and the type of the device, and a control section for controlling the storage section so that communication with the communication party is established based on the table. The control section transmits the second identification information and type of the device to unspecified destinations with predetermined timing, and updates the table based on second identification information and type of the communication party which are sent back as a response from the communication party.