By synthesizing the map of an entire network, it provides a method for detecting OSI Reference Model layer-2 switches and evaluating the status of the inter-connection of the layer-2 switches. The NMT (102) which implements the SNMP manager queries the specified management IP-addresses and receives responses from the SNMP agents implemented on the layer-2 switches (103,104,105). From the management information in the responses, the existence of the layer-2 switches is confirmed and the MAC address and port information mapping table MvP table is constructed. Based on the MvP table the inter-connection information of the layer-2 switches is detected.