An object is to provide a motor-incorporation-spindle ball bearing capable of allowing cooling air which enters inside the bearing of the motor-incorporation-spindle to be discharged smoothly out of the bearing without causing turbulent flow inside the bearing, does not cause a retainer easily to be vibrated, and provides a high level of silent operation. A seal plate has a length to allow air to pass through the bearing from an entrance side toward an exit side substantially straightly without resistance. Therefore, the seal plate is less likely to be exposed to unnecessary force when the air passes through the bearing; the seal plate is prevented from wobble and deformation; stable sealing is ensured; the air is discharged smoothly without causing turbulent flow inside the bearing; a retainer is not easily vibrated, and silent operation is maintained.