A wheel bearing apparatus comprising: an outer member integrally formed on its outer circumference with a body mounting flange adapted to be mounted on a knuckle of a suspension apparatus and on its inner circumference with double row outer raceway surfaces (2a, 2a); an inner member including a hub wheel (4, 4', 31) and at least one inner rings (5, 7), the hub wheel (4, 4', 31) being integrally formed on its one end with a wheel mounting flange and with a cylindrical portion axially extending from the wheel mounting flange, the inner rings (5, 7) being press-fitted onto the cylindrical portion of the hub wheel (4, 4', 31) via a predetermined interference and formed on their outer circumferences with inner raceway surfaces (5a, 5a) corresponding to the outer raceway surfaces (2a, 2a) of the outer member; and double row rolling elements (3, 3) freely rollably contained between the inner and outer raceway surfaces (5a, 5a; 2a, 2a) of the inner and outer members (1, 2) via cages (8, 8) wherein a hardened ring-shaped gear member is mounted on an end of the cylindrical portion of the hub wheel (4, 4', 31), the gear member being formed on its outer circumference with a gear portion and on its inner circumference with a splined portion engaging a hub-splined portion (25, 25') formed on the outer circumference of the cylindrical portion of the hub wheel (4,4', 31); wherein both a contacting surface of the gear member and a contacting surface of the inner ring being abutted against each other are ground; and wherein the inner rings (5, 7) are axially immovably secured under a condition in which a predetermined amount of a bearing pre-stress is applied to the inner rings (5, 7) via the gear member characterized in that the surface roughness (Ra) of the contacting surface of the gear member contacted against the inner ring is set to 1.6 or less (Ra≦1.6), in that an external thread is formed on the end of the cylindrical portion of the hub wheel, and in that a securing nut is fastened on the external thread to secure the inner rings (5, 7). an outer member integrally formed on its outer circumference with a body mounting flange adapted to be mounted on a knuckle of a suspension apparatus and on its inner circumference with double row outer raceway surfaces (2a, 2a); an inner member including a hub wheel (4, 4', 31) and at least one inner rings (5, 7), the hub wheel (4, 4', 31) being integrally formed on its one end with a wheel mounting flange and with a cylindrical portion axially extending from the wheel mounting flange, the inner rings (5, 7) being press-fitted onto the cylindrical portion of the hub wheel (4, 4', 31) via a predetermined interference and formed on their outer circumferences with inner raceway surfaces (5a, 5a) corresponding to the outer raceway surfaces (2a, 2a) of the outer member; and double row rolling elements (3, 3) freely rollably contained between the inner and outer raceway surfaces (5a, 5a; 2a, 2a) of the inner and outer members (1, 2) via cages (8, 8) wherein a hardened ring-shaped gear member is mounted on an end of the cylindrical portion of the hub wheel (4, 4', 31), the gear member being formed on its outer circumference with a gear portion and on its inner circumference with a splined portion engaging a hub-splined portion (25, 25') formed on the outer circumference of the cylindrical portion of the hub wheel (4,4', 31); wherein both a contacting surface of the gear member and a contacting surface of the inner ring being abutted against each other are ground; and wherein the inner rings (5, 7) are axially immovably secured under a condition in which a predetermined amount of a bearing pre-stress is applied to the inner rings (5, 7) via the gear member characterized in that the surface roughness (Ra) of the contacting surface of the gear member contacted against the inner ring is set to 1.6 or less (Ra≦1.6), in that an external thread is formed on the end of the cylindrical portion of the hub wheel, and in that a securing nut is fastened on the external thread to secure the inner rings (5, 7).