A magnetized layer (12) is integrally bonded to an annular holder (11) installed to a rotating body, the magnetized layer is made of a material obtained by mixing a magnetic fine particle to a rubber elastic material or a synthetic resin material and magnetized in a multipolar manner at a predetermined pitch in a circumferential direction, and a portion having a different sectional shape from the other portions is formed in a part in a circumferential direction in a joining part of the holder (11) with the magnetized layer (12), by a raised part (11c) or the like, so that a significant point of a signal level is formed in this portion on the basis of a difference in a magnitude of a magnetic field, whereby the significant point is set to a rotation angle measurement starting point.
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