Communicating method between IPv4 terminal and IPv6 terminal and IPv4-IPv6 converting apparatus

A method for notifying a first terminal (5) using IPv6 as a communication protocol of an address of a second terminal (2) using IPv4 as a communication protocol, comprising the steps of: sending a first message inquiring for an IP address of said second terminal to a manager apparatus which manages address information, said first message being created by said first terminal; receiving a second message containing an IPv4 address of said second terminal sent from said manager apparatus in response to said first message; converting said IPv4 address of said second terminal into an IPv6 address corresponding to said IPv4 address of said second terminal; and sending a third message containing the IPv6 address resulting from the converting step to said first terminal; wherein said first message sending step further comprises the substeps of: sending said first message to a first manager apparatus which manages IPv6 address information; and sending said first message to a second manager apparatus which manages IPv4 address information, if said second message is not received from said first manager apparatus within a predetermined time.