Here, when there is a fault in an optical fiber connecting the B/R band coupler C1 to the B/R band coupler R11, optical signals are inputted/outputted thereto/therefrom through the first 1???2 optical switch and the B/R band coupler C2, and when there is a fault in an optical fiber connecting the B/R band coupler C2 to the B/R band coupler R21, optical signals are inputted/outputted thereto/theref