LOOP NETWORK DEVICE

PURPOSE:To communicate through a reserve loop at a time when both main and reserve loops are normal by providing a change-over switch in accordance with priority order between a communication control part containing terminals of low-order priorities and a loop interface part. CONSTITUTION:In case the loop transmission lines 4, 5 are both normal, the interface parts 6, 7 are connected to the communication control parts 10, 11 by the change-over switch part 8, but if a fault occurs on the optical fiber 4 side, the switch 8 switches so that the interface 7 and the control part 10 which is connected to a terminal of a high importance are connected with each other, and thus the communication with the terminal connected to the control part 10 is secured. In case a fault occurs on the optical loop 5 side, the switch 8 remains as it is, and the communication with the terminals of less importance connected to the control part 11 is cut off, and thus the communication through the control part 10 is secured.