To simplify fault recovery processing by eliminating analysis of control information in nodes on the way of a communication route.

When a fault of a path 1 is detected on the basis of the intensity reduction of an optical signal which is branched and taken in by a node device #E on the reception side out of two node devices #A and #E, output of at least an optical signal to be inserted out of optical signals which can be inserted to or pass another path 2 having the same combination as the faulty path 1 is stopped, and router part 20 uses paths 3 and 4 of the other combination for two-way communication instead of the present combination having the faulty path 1.