A ball bearing lubricated by lubricating oil, comprising: an inner ring including an inner ring raceway groove on an outer circumferential surface thereof; an outer ring including an outer ring raceway groove on an inner circumferential surface thereof; and a plurality of balls rollably arranged between the inner ring raceway groove and the outer ring raceway groove , wherein the outer ring includes at least one radial hole that extends radially through the outer ring from an outer circumferential surface thereof to the inner circumferential surface thereof; and a counter bore is provided on the inner circumferential surface of the outer ring ; characterized in that the counter bore includes an inclined portion (12b1) that gradually decreases in diameter from an axial end surface toward the outer ring raceway groove , and a straight portion (12b2) that connects the inclined portion (12b1) and the outer ring raceway groove and that is parallel to a centerline (L) of a rotation axis of the ball bearing ; and that when a minor angle formed relative to a rotation axis (s) of the ball by a straight line that connects a center (O) of the ball and an intersection point between a centerline (X) of the radial hole and a surface of the ball is defined as λ, an axial position of the centerline (X) of the radial hole is set to satisfy a relationship of 0° < λ ≤ 60°, wherein the rotation axis (s) of the ball is a rotation axis when the ball rolls on the outer ring raceway groove and the inner ring raceway groove during the rotation of the ball bearing , and forms an angle of substantially 90° with respect to a line representing the contact angle α. an inner ring including an inner ring raceway groove on an outer circumferential surface thereof; an outer ring including an outer ring raceway groove on an inner circumferential surface thereof; and a plurality of balls rollably arranged between the inner ring raceway groove and the outer ring raceway groove , wherein the outer ring includes at least one radial hole that extends radially through the outer ring from an outer circumferential surface thereof to the inner circumferential surface thereof; and a counter bore is provided on the inner circumferential surface of the outer ring ; characterized in that the counter bore includes an inclined portion (12b1) that gradually decreases in diameter from an axial end surface toward the outer ring raceway groove , and a straight portion (12b2) that connects the inclined portion (12b1) and the outer ring raceway groove and that is parallel to a centerline (L) of a rotation axis of the ball bearing ; and that when a minor angle formed relative to a rotation axis (s) of the ball by a straight line that connects a center (O) of the ball and an intersection point between a centerline (X) of the radial hole and a surface of the ball is defined as λ, an axial position of the centerline (X) of the radial hole is set to satisfy a relationship of 0° < λ ≤ 60°, wherein the rotation axis (s) of the ball is a rotation axis when the ball rolls on the outer ring raceway groove and the inner ring raceway groove during the rotation of the ball bearing , and forms an angle of substantially 90° with respect to a line representing the contact angle α. <EOS>