To realize a structure capable of improving sealability, being miniaturized and lightened, and corresponding to modifications of attaching positions of an encoder and a sensor as needed for contributing to improving the degree of freedom in design.

The encoder 7a made of a permanent magnet is annexed to an outer face of a circular ring part 14 of a slinger 8a composing a combined seal ring 6a. An outer face of the encoder 7a is covered by a cover plate 19 made of non-magentic material. This cover plate 19 prevents foreign matter adhesion and damage to the encoder 7a. A seal lip 16b is provided slidably contacting an inner face of the circular ring part 14 of the slinger 8a.