A communication network management system has: a communication network including a plurality of nodes and a plurality of links connecting between the plurality of nodes; and a management computer connected to the plurality of nodes. A loop-shape communication route in the communication network is a loop route. The management computer transmits a frame to one node on the loop route. When receiving the frame, each node on the loop route forwards the received frame to a subsequent node along the loop route and, if a predetermined condition is satisfied, returns a response back to the management computer. The management computer determines whether or not a failure is occurring, based on reception state of the response.