The optical communication system of the present invention is constructed with a data plane and a control plane, and includes a first monitor for monitoring a path alarm on the data plane, a second monitor for monitoring a path alarm on the control plane, and an alarm comparator for comparing alarm statuses of the optical paths that the first monitor and the second monitor preserve, wherein an optical communication apparatus, of which the first monitor and the second monitor both are in a status of having detected the alarm, operate so as to start an operation of avoiding a fault. Such a configuration makes it possible to make a detour only around an appropriate section including a fault location without performing an erroneous operation when a fault has occurred in an optical path, in which a plurality of detour sections, in an all-optical communication system.