Abstract: The object is to realize a multi-line service with proprietary messages/procedures only between telephone apparatuses such as IP telephones, and to use a connection management server complying with a standard connection protocol without using proprietary messages/procedures between the connection management server such as the SIP server and the telephone apparatus. A telephone apparatus for performing a telephone call using a predetermined communication protocol and a connection protocol, includes: a unit configured to mutually report a line status using a proprietary interface different from the connection protocol between the telephone apparatus and another telephone apparatus forming a multi-line group.