The present invention provides a VoIP wireless telephone system utilizing a wireless LAN wherein expansion of an IP wireless extension telephone is realized while ensuring secrecy of talk in a VoIP service. In the system, ID and password for connection to the Internet by PPPoE are set to a wireless LAN terminal; user authentication is executed with the above information upon connection to a BAS through a DSLAM; an ADSL modem transmits, to the BAS, IP frames received from the wireless LAN terminal; and after connection by PPPoE an IP address is given from the BAS to the wireless LAN terminal. ID and password for connection to an SIP server and the URL of the SIP server are registered in the wireless LAN terminal; connection from the wireless LAN terminal to the SIP server is made on the basis of the above connection information and the telephone number of the connection destination designated by a telephone; and the ADSL modem transmits, to the SIP server, IP frames received from the wireless LAN terminal to thereby establish a session to the telephone talk destination.