Attachment holes are formed in a plurality of locations in the circumferential direction of the attachment flange of a wheel bearing unit. The amount “h” of projection, from an attachment surface in the axial direction of the opening edge peripheral portion of the respective attachment holes is limited to no larger than 10 μm under the condition that studs are press-fitted and fixed into the respective attachment holes. By this configuration, it is possible to inhibit the runout of the rotor fixed to the attachment surface of the attachment flange and thereby inhibit the judder generated during braking operation.