To provide a wheel bearing with rotational speed detector improved in detection precision and reliability while inhibiting foreign matter from invading by enhancing the sealing performance of the detecting part while intending to downsize.

The sensor holder 10 comprises: the holder part 12 of synthetic resin in which the rotational speed sensor 14 is embedded; and the cover 11 comprising the cylindrical fitting part 11a for externally fitting with the end of the external member 5, the flange part 11b extending radially inward for being brought into close contact with the end part of the external member 5, and the bottom 11c extending radially inward. The holder part 12 is formed in a shape along the profile of the shoulder 23 of the external joint member 22, where the shoulder 23 is opposite to the holder part 12 through the clearance for constituting the labyrinth seal 26, also the holder part 12 is arranged on the radially outward one point of the bottom 11c in the vertical direction of the road surface in an inclination range of 30-90. From the holding part 12 the harness 21 is extending in the tangential direction of the cover 11.