To provide a bearing unit having a hub bolt mounting structure hardly causing looseness of a hub bolt, and hardly causing rupture of the hub bolt even when an unexpected impact load is input to a disk wheel.

This bearing unit includes: a stationary ring (outer ring) 2 fixed to the side of a vehicle body; a rotational ring (inner ring) 4 to which components on the side of a wheel (a brake rotor BR and a disk wheel (aluminum wheel) DW) arranged oppositely to the outer ring and arranged on the side of the wheel are fixed, and rotated together with the wheel; and rolling elements 6, 7. The bearing unit has a structure provided with a disk-shaped hub flange 12a extending outward from the side of the vehicle body of the inner ring and positioning the components on the side of the wheel, and a hub bolt hole 12a arranged at a predetermined interval along the peripheral direction of the hub flange, so that the hub bolt 14 is pressure-fitted into the hub bolt hole toward the side of the wheel. An elastic body (spring washer) 15 is interposed between the surface S1 of the hub flange on the side of the vehicle body and the head part 14b of the hub bolt.