PURPOSE: To prevent the entire system from being faulty even at disconnected cable by transmitting a signal to be transmitted to a loop transmission line possible for selecting one of two systems and selecting the systems by a switch installed on a reception point.

CONSTITUTION: A connecting terminal is provided to points (a)∼(j) and the connection terminals are connected in a loop by the optical fiber 1. In relaying a signal between the positions (a) and (f), a TV camera 2 and a repeater 3 are moved to the position (a), and the repeater 3 is connected to both the terminals by releasing the connection of both the terminals. Further, a TV monitor 4 and a relay circuit 5 are arranged on the position (f) and the repeater 5 is connected to both the terminals by releasing the connection of both the terminals. The repeater 3 uses a control signal from the controller 7 to select one of two terminals and transmits a signal. The repeater 5 uses the control signal similarly to select the line transmitted from the point (a) and then receives a signal.