A CPU of an IP telephone apparatus transmits, to an ENUM server, a message "Request the NAPTR record" corresponding to the destination terminal. The CPU also receives a message "Respond to the NAPTR information" in response to the message "Respond to the NAPTR record". Further, the CPU automatically transmits, from a network I/F to the ENUM server, the request for the registration of information regarding the apparatus terminal when the switch is initially turned ON after the IP telephone apparatus is installed and connected to the IP network. The request for the registration is previously stored in a memory. The CPU also receives the message "Respond indicating completion of the registration" in response to the request for the registration.