PURPOSE: To recover the trouble of a communication control part in a short time, by connecting additionally a communication address line at every line, and providing an address latch at every communication control part, and standby communication control part.

CONSTITUTION: Each of lines 1...1d is accommodated in a line connection panel 5. Enable lines 9a...9d and the communication address lines 10a...10d are connected additionally by the line connection panel 5, and are connected to the communication control parts 3a...3d respectively through panel cables 6a...6d. The communication centrol parts 3a...3d to which the panel cables 6a...6d are connected, become enabled, and latch the addresses connected to the communication address lines 10a...10d as the address of its own station, at address latches 8a...8d. By changing the connection of the panel cable 6a to the standby communication control part 3e, the communication control part 3a in which the trouble is generated, is disenabled, and separated, and the standby communication control part 3e becomes enabled, and also, the address of its own station becomes the line address of the line 1a.