To collectively manage user networks connected to a virtual private network (VPN) without such time and effort necessary for an operation management server to be ready for an expansion MIB for each of vendors. Provided is a network management system, including: a first edge router, an operation management server and a second edge router which connects to the first edge router, the second edge router being included in the network constituted for each of the user groups, wherein the first edge router includes: collecting unit for collecting management information regarding constituent elements of the network constituted for each of the user groups from the second edge router on the network constituted for each of the user groups, unit for storing the management information in correspondence with the virtual private network for each of the user groups, and unit for returning the management information when receiving, from the operation management server, a request for the management information brought in correspondence with the virtual private network for each of the user groups, and the operation management server includes requesting unit for designating the virtual private network for each of the user groups and requesting the first edge router to return the management information regarding the constituent elements of the network constituted for each user group connected to the virtual private network.