The network relay device is provided. The network relay device includes: a plurality of ports, each being configured to be connectable with one physical line; a virtual line controller configured to treat a plurality of physical lines, which are respectively connected with the plurality of ports, to constitute a virtual line; and a status check frame controller configured to send via the virtual line a status check frame for use in checking status of a network, which the network relay device is connected with via the virtual line, wherein the status check frame controller changes a frame-sending port to be used to send a next status check frame, in order to avoid continuously using an identical port as both a frame-sending port to send the status check frame and a frame-receiving port to receive the status check frame from another network relay device.