To provide a remote maintenance method of a network in which a network being imparted with an IP address dynamically can be maintained remotely.

In a service network 10, a maintenance unit 20 delivers an INVITE request 30 including discrimination information for maintenance, supplies an SIP-VoIP gateway 12 with an INVITE request 32 through an SIP proxy server 18, judges whether it is an INVITE request for acquiring an address or not based on the supplied discrimination information for maintenance and the discrimination information held in a maintenance object unit, creates an error response 38 containing an address currently set in the SIP-VoIP gateway 12 depending on decision of the acquisition request, supplies it to the maintenance unit 20 through the SIP proxy server 18, and extracts the address from an error response 40 received by the maintenance unit 20.