BEARING DEVICE FOR WHEEL

[Object] A wheel bearing apparatus is provided in which penetration of rain water or dust and leakage of a differential gear oil are prevented and thereby sealing effect is increased, and reliability is ensured over the long term. [Solution] In a wheel bearing apparatus of a semi-floating type, a pilot portion 21 of an outer member 20 is configured of a cylindrical portion 21a extending from a body mounting flange 4b and a tapered portion 21b gradually decreasing in its diameter from the cylindrical portion 21a to an end surface of the inboard side. A fitting portion 16 of an axle housing 14 is formed corresponding to a shape of the pilot portion 21 of the outer member 20, and an annular groove 22 having a rectangular cross-section is formed at the tapered portion 21b of the pilot portion 21 and a seal ring 23 formed of a synthetic rubber is mounted in the annular groove 22. An outer diameter d3 of the seal ring 23 after mounting is set to be smaller than an inner diameter d4 of the cylindrical portion 16a of the axle housing 14 and then elastically contacts the axle housing 14. A slight gap of a fitting portion between the outer member 20 and the axle housing 14 is blocked off.