A method for controlling switching in a bidirectional line-switched ring network configured by a plurality of optical fibers and a plurality of nodes, (i) having a first node receive as input an LP-S (or having the first node detect an SF-P) and having a second node adjacent to the first node across a span receive the LP-S (or receive the SF-P), and (ii) having the second node send an SF-R switch request to another node when the second node further detects an SF-R on said span under the above state (i), whereby a method for controlling switching in a bidirectional line-switched ring under conditions where ring switch and LP-S cannot co-exist, but ring switch and SF-P can, is realized, as a whole, in the ring network.