Abstract: An apparatus for detecting elongation of the joint of a conveyor belt has a pair of sensors, each of which includes an iron core having a coil winding therearound and being spaced at a predetermined distance from each other parallel with the conveyor belt and which distance is greater than the length of the joint along the belt. A pair of magnetic elements is fixed to the underside surface of the belt, the magnetic elements being spaced from each other a distance equal to the distance between the sensors when the joint is unelongated, so that said sensors and elements are aligned during movement of the conveyor belt past the sensors.