A CPU in an IP telephone apparatus automatically controls to transmit, from a network I/F to an ENUM server, a request for deleting a NAPTR record when an absent key is pressed. The CPU regularly transmits, from the network I/F to the ENUM server, an inquiry for a NAPTR record of another IP telephone apparatus. When the CPU receives, from the ENUM server via the network I/F, a response indicating that the NAPTR record of another IP telephone apparatus has been deleted, in response to the inquiry, the CPU turns OFF a lamp indicating that the user is available.