In an overlay network system in which at least one node is mapped in a hash space by distributed hash table techniques, each node having a nods identifier obtained by hashing identification information of the own node, at least one service concerning all the nodes is provided. Each node includes a storage unit and a controller. The storage unit stores a service name and a service body of the service. The controller searches for a current service provider node using a service key obtained by hashing the service name, checks whether the own node is allowed to take over the service if a distance between the node identifier of the own node and the service key is less than a distance between the node identifier of the current service provider node and the service key, and invokes the service body to provide the service if the takeover is permitted.