Network management system and management computer

Provided is a network management system for managing a plurality of packet relay devices, the network management system comprising: the plurality of packet relay devices constituting networks; and a display device for displaying configurations of the networks, in a case where it is determined that a virtual packet relay device identifier of the virtual packet relay device that is assigned a second-network identifier associated with the extracted second-network identifier is registered in a first-network configuration table, a first-work identifying module is configured to associate a first-network identifier that is associated with the virtual packet relay device identifier with the obtained configuration information, and register the association between the first-network identifier and the obtained configuration information in the first-network configuration table.