Abstract: At each of a plurality of points of embedment in a conveyor belt, a set of at least two detectable elements is embedded, and a control unit is arranged (a) to receive and process signals from an externally installed sensor, the signals having a varied intensity corresponding to the number of detectable elements in a given embedment point, (b) to average the intensities of a plurality of the signals for the given embedment point, and (c) to judge, on the basis of the average obtained in (b), the presence or absence of a breakage of detectable element or elements at the given embedment point. The abovementioned arrangement is able to judge whether one of the two detectable elements is broken, and the judgment is not affected by variation of the distance between detectable elements and the sensor. If breakage of a single detectable element of any set is identified, the affected element may be repaired during an outage of the conveyor.