RETAINER OF BALL BEARING

In a grease filled bearing for a machine such as a turbo molecular pump that rotates at high speed, objects are to prevent grease retained in an inner circumferential part of a ball retainer from being forced out to the outside of the bearing due to centrifugal force, thereby achieving extension of the operational life of the bearing, and preventing occurrence of rotational mass unbalance due to the grease forced out. A retainer (1) of a ball bearing includes a main body (1A) having a circular annular shape, and plural circular pockets (1a) for retaining balls (4) therein that extend through the main body (1A) in a radial direction, wherein intermediate parts between adjacent pockets (1a) in an inner circumferential surface of the main body (1A) define recesses (1b) for holding grease.