A relay system for relaying an APS (Automatic Protection Switching) packet in a n MC-LAG (Multi-chassis LAG) network having a first boundary node and a second boundary node as well as a third boundary node and a fourth boundary node provided opposing to the first boundary node and the second boundary node and connected by logic line paths, characterized in that the first boundary node comprises: a notification unit (53A, 53B) adapted to use a second path connected to the fourth boundary node to notify the fourth boundary node of state information indicating a state of a first path connected to the third boundary node, the third boundary node comprises: a notification unit adapted to use,a third path connected to the fourth boundary node to notify the second boundary node of state information indicating a state of the first path, the second boundary node and the fourth boundary node comprise: an APS processing unit (53A, 53B) adapted to use a fourth path connected between the second boundary node and the fourth boundary node to exchange the state information notified from the first boundary node with the state information notified from the third boundary node; and a switching unit (55, 56, 57, 58) adapted to, when the state information notified from the first boundary node and the state information notified from the third boundary node are information (SF-W) indicating a failure state of the first path that is an active path and when the self apparatus is one responsible for a switching, switch the active path to a backup path that is the second path or the third path connected to the self apparatus. a notification unit (53A, 53B) adapted to use a second path connected to the fourth boundary node to notify the fourth boundary node of state information indicating a state of a first path connected to the third boundary node, the third boundary node comprises: a notification unit adapted to use,a third path connected to the fourth boundary node to notify the second boundary node of state information indicating a state of the first path, the second boundary node and the fourth boundary node comprise: an APS processing unit (53A, 53B) adapted to use a fourth path connected between the second boundary node and the fourth boundary node to exchange the state information notified from the first boundary node with the state information notified from the third boundary node; and a switching unit (55, 56, 57, 58) adapted to, when the state information notified from the first boundary node and the state information notified from the third boundary node are information (SF-W) indicating a failure state of the first path that is an active path and when the self apparatus is one responsible for a switching, switch the active path to a backup path that is the second path or the third path connected to the self apparatus. a notification unit adapted to use,a third path connected to the fourth boundary node to notify the second boundary node of state information indicating a state of the first path, the second boundary node and the fourth boundary node comprise: an APS processing unit (53A, 53B) adapted to use a fourth path connected between the second boundary node and the fourth boundary node to exchange the state information notified from the first boundary node with the state information notified from the third boundary node; and a switching unit (55, 56, 57, 58) adapted to, when the state information notified from the first boundary node and the state information notified from the third boundary node are information (SF-W) indicating a failure state of the first path that is an active path and when the self apparatus is one responsible for a switching, switch the active path to a backup path that is the second path or the third path connected to the self apparatus. an APS processing unit (53A, 53B) adapted to use a fourth path connected between the second boundary node and the fourth boundary node to exchange the state information notified from the first boundary node with the state information notified from the third boundary node; and a switching unit (55, 56, 57, 58) adapted to, when the state information notified from the first boundary node and the state information notified from the third boundary node are information (SF-W) indicating a failure state of the first path that is an active path and when the self apparatus is one responsible for a switching, switch the active path to a backup path that is the second path or the third path connected to the self apparatus.