To provide a bearing device for a wheel improving the fatigue life around a corner portion between a wheel attaching flange and pilot portion, suppressing increase of deflection due to the generation of crack, controlling lowering of steering stability, and decreasing weight; and provide a surface processing method therefor.

The bearing device A for a wheel has an inner member 2 and an outer member 1 which are rotatable each other through a plurality of plural lines of rolling elements 3. The inner member 2 or the outer member 1 has the wheel attaching flange 1a, and the pilot portion 1b guiding a brake or a wheel from a base portion of the wheel attaching flange 1a to an outboard side is projected out. At the corner portion 1c between a side surface of the wheel attaching flange 1a and an outer peripheral surface of the pilot portion 1b, remaining reaction force is generated by composite shot peening using shot particles having different particle diameters, and surface hardness is made to be harder than base material hardness.