To possibly reduce a distance between a magnetoresistive element and teeth of a gear, and improve the detection accuracy of rotations of a rotating body.

Since the magnetoresistive element (MRE) 31 is disposed so as to have a predetermined length in the thickness direction of a substrate 30, a sensing axis of the MRE 31 is not set in the direction along a surface of the substrate 30, and is set in the thickness direction of the substrate 30. The substrate 30 can be disposed so as to cause its surface to face the teeth 21 of the gear. The distance between the MRE 31 and the teeth 21 of the gear can be reduced.