To prevent the disconnection of a harness for taking out a detection signal of a sensor by preventing an outer ring for supporting the sensor from rotating relative to a housing.

An outer ring 1 press fitted in the inner diameter side of a housing 20 is held by being interlaid between a locking collar part 21 and a segmental ring-shaped retaining ring 23 locked in an locking groove 22 of the housing 20. Also, a part of an engaging pin 25 installed on the end face of the outer ring 1 is engaged in the interval part between circumferential-direction both end faces 24 of the retaining ring 23. When the outer ring 1 is about to rotate relative to the housing 20, a part of the engaging pin 25 is bumped and fixed with either one end face 24 of the retaining ring 23.