An embedded body including, at one end portion of a coaxial cable, one side antenna unit and an IC tag that is passive and connected to the one side antenna unit, and another side antenna unit at the other end portion of the coaxial cable is embedded in a conveyor belt. The one side antenna unit and the IC tag, and the other side antenna unit disposed with an interval in a width direction and the coaxial cable is embedded extending in the width direction. A calculation unit determines whether a detector has received a radio wave emitted from the IC tag through the coaxial cable and the other side antenna unit in response to a radio wave emitted from the detector, and then whether a vertical tear has been generated in the conveyor belt based on the determination result.