A wear detection device for a conveyor belt capable of automatically, easily, and accurately detecting the wear amount of the conveyor belt during the operation, formed in a simple structure, and manufacturable at low cost. A rubber magnet (3) magnetized in the thickness direction is buried in the conveyor belt (2) diagonally relative to both the advancing and thickness directions of the conveyor belt. A magnetic sensor (4) detecting the change of a magnetic force due to the wear of the rubber magnet (3) resulting from the wear of the conveyor belt (2) is disposed at a position through which the rubber magnet (3) is passed.