A filter-information transmitting/receiving unit transmits path information with the filter information when the filter information is set by a filter setting unit, and receives the path information when the filter information is set in other network device. A filter-combining determining unit determines whether redundant filter information with the other network device is to be combined or deleted, based on the filter information and the path information. A filter control unit issues a filter-setting request or a filter release request based on a result of determination by the filter-combining determining unit.