On the basis of information of a topology map, a parent node ID list is generated to show correspondence of ID of each node to that of its parent node. Information given by the parent node ID list is transmitted as connection display data in a predetermined format. The receiving side, on the basis of the received connection display data, obtains information of a connecting status display to display connecting status of a network. On the basis of this information, a display to show connecting status of the network is displayed.