Abstract: Among systems configured by connecting a plurality of sequence controllers to one communication line to intercommunicate, many systems has been disclosed which implement fault location and recovery from the faults. In one of these systems, each substation is connected to a circulating communication line via a branch line and switches are respectively disposed on the branch line and on the communication line at both sides of a connecting point of the branch line and the communication line. Further, the communication line can be formed in a loop by a spare line. In another of these systems, an integrated portion of the communication line is formed near the master station, and the communication line is connected to the master station and is configured of one continuous line which goes and backs in sequence between the integrated portion and vicinity of each substation. In that integrated portion, a switch is disposed on each one of two lines, which connect the integrated portion and each substation.