When protection processing is applied after a fault in the optical switching unit while the path control unit is restarting. In network systems comprising a path control unit for setting the paths, and a data transmission unit coupled to the path control unit; the data transmission unit changes the path information, stores path information before and after the fault was detected, and transmits the path information from before or after fault detection to the path control unit, and decides either of the transmitted path information based on an internal status; and the path control unit stores the path information sent from the data transmission unit, and after restarting, receives path information from the data transmission unit and, acquires path information stored in the path control units controlled by the adjacently connected data transmission units and is restored to operation with path information from before restarting.