NETWORK MONITORING DEVICE AND NETWORK MONITORING METHOD

In order to quickly estimate an abnormal transponder at low cost, a network monitoring device acquires, when sensing a failure occurrence channel, route information of the failure occurrence channel. The network monitoring device generates an adjacent channel table in which an adjacent channel being close in wavelength to the failure occurrence channel is extracted, then generates an interference channel table in which an interference channel sharing a common route with the failure occurrence channel among the adjacent channels is extracted, and then performs weighting on the interference channel, based on closeness of wavelength to the failure occurrence channel, and generates an influence channel table in which a weight is given to the interference channel. The network monitoring device estimates, based on the influence channel table, a channel with a large weight to be a channel having a possibility of exerting a negative influence on the failure occurrence channel.