Disclosed is a synchronous ring network system, which has a plurality of nodes, each of the nodes has: switching means for conducting a protection switching processing in response to a trouble; higher-order path misconnection search means for searching a misconnection of the AU signal caused by the switching processing; means for instructing the higher-order path squelch means to squelch an AU signal from the result of the higher-order path misconnection searching: lower-order path misconnection search means for searching a misconnection of the TU signal caused by the switching processing; means for instructing the lower-order path squelch means to squelch a TU signal from the result of the lower-order path misconnection searching; means for instructing the release of the higher-order path squelch after squelching by the lower-order path squelch means; and means for instructing the higher-order path overhead processing means to stop the termination as to a predetermined byte of each byte for composing the higher-order path overhead.