A slinger has a substantially L-shaped cross-section and includes a rotating cylindrical portion and a rotating circular ring portion. An inner circumferential surface of the rotating cylindrical portion is a stepped cylindrical surface in which a large-diameter portion formed at a portion close to the rotating circular ring portion and a small-diameter portion formed in the remainder are continuously connected by a stepped portion. The encoder supported by the rotating circular ring portion is formed by solidifying and securing a molten permanent magnet material in a state that a molding die collides with the stepped portion. An outer diameter of a hub is defined as φD, an inner diameter of the small-diameter portion in a free state is defined as φd1, and an inner diameter of the encoder in a free state is defined as φd2, a relationship of φd1≦φd2