It is possible to identify a communication range even for a communication across a plurality of VLAN in a network having a plurality of communication paths because of a redundant switch configuration when managing switch VLAN setting information. A device having a predetermined VLAN-ID is made to be a KEY and a device having a predetermined VLAN-ID which can perform communication from the device is made to be a VALUE. A VLAN communication enabled/disabled hash table is created for expressing each of KEYs and VALUEs as a set of a device name and a VLAN-ID. By referencing a redundant configuration table indicating a redundant configuration and a routing table indicating whether routing is enabled, form a KEY specified as a start point for a network administrator, a VALUE which can be communicated from the KEY is identified and the VALUE is used as a KEY to follow a path.