An advertisement search agent detects a service that is provided by a node or a service that can be used by a node immediately after the node is newly connected to a domain. A message acquisition unit acquires an advertisement search message broadcast or multicast by a node connected to either one of a plurality of domains. A message database stores advertisement search messages acquired by the message acquisition unit. A node connection monitoring unit detects the connection of a node to either one of a plurality of domains. When the connection of a node is detected by the node connection monitoring unit, a delivery message extractor extracts an advertisement search message stored in the message database. A message delivery unit delivers the advertisement search message extracted by the delivery message extractor.