An internet protocol address converting apparatus has an address acquiring unit for acquiring a first private IP address in a first IP address format by connecting to a DHCP server that dynamically allots the IP address, and also acquiring a second private IP address for the second terminal; a network address providing unit for allotting the second terminal with a network address to generate a global IP address; a storing unit for storing a mapping table, the mapping table saving the second private IP address of the second terminal and the global IP address; an address converting unit for converting the second private IP address into the global IP address; and a control unit for performing an announcing, requesting a registration of the second terminal to a master server.