Retainer for angular contact ball bearing, angular contact ball bearing, and hub unit bearing

A retainer for an angular contact ball bearing comprising:

• an annular rim portion;
• a plurality of pillar portions extending from a plurality of locations in a circumferential direction of the rim portion to an axially one side, each having concave curved side surfaces in the circumferential direction;
• a plurality of pockets respectively defined by a portion surrounded on three sides by a pair of pillar portions adjacent to each other in the circumferential direction of the plurality of pillar portions and the rim portion;
• and
• the pillar portions respectively having a notch in a range extending from an end section on the axially one side to an axially intermediate section to communicate the pair of pockets adjacent to each other in the circumferential direction,
• wherein the notch has a rectangular, trapezoid, or trapezium opening shape as seen from the circumferential direction, and an inner surface of the notch has a radially outer side flat surface portion arranged on a radially outer side from a center of each of the pockets and extending substantially linearly in an axial direction, a radially inner side flat surface portion arranged on a radially inner side from the center of each of the pockets and extending substantially linearly in the axial direction, and a back side flat surface portion arranged on an axially other side from the center of each of the pockets and extending linearly in a radial direction, and
• wherein the back side flat surface portion has a constricted shape in which an intermediate section in a length direction thereof is narrower than both side portions in the length direction thereof.