A magnet is disposed on one face of a hollow section which is the conveyance path of an object of detection, and has a magnetic pole of designated length along the conveyance direction of the object of detection. A magnetic body is disposed along the conveyance direction opposite the magnet with the hollow section therebetween, and generates a cross magnetic field that crosses the hollow section formed between the magnetic body and the magnet. An anisotropic magnetoresistance element is disposed on the side of the magnetic body carrier facing the hollow section, and has magneto-sensing action in the conveyance direction.