PURPOSE: To receive a bypass release command from a central processing equipment even in a bypass state, by connecting so that a receiving input can be received at all times, in case a transmission terminal in a loop transmission system is bypassed from a transmission line at the time of a fault.

CONSTITUTION: When a fault occurs in a transmission device connected to a loop transmission line 4, a bypass command is sent to the transmission device through the transmission line 4 from a central control device which is not shown in the figure, and this bypass command is made to branch by a branch device 11. Subsequently, it is decoded to be a bypass command, by a monitor signal decoding part 15, and a contact of a switch part 7 is changed over to the side D. Accordingly, a faulty station is separated from the loop transmission line 4, and is not obstructive to an operation of other normal station. On the other hand, when a release command to the faulty station is sent onto the loop transmission line, in the same way as said processing, this command is made to branch by the branch device 11, is decoded to be a bypass release command by the decoding part 15, and the contact of the switch part 7 is changed over to the side C.