Retainer and ball bearing

In the retainer in which a corner part and a ring part are integrally molded by synthetic resin, the deformation of the corner part caused by centrifugal force and the reduction of the strength of a weld seam are both suppressed. The ring portion (7) has a pocket bottom (9) located on the outermost side of the pockets (12) in the axial direction. The corner section (8) has: a base section (10) extending between the pockets (12) and connected to the ring section (7) in the axial direction; and a pair of claws (11a, 11b) separated from each other. Each of the claws (11a, 11b) has a pocket inner surface (13) on the pocket (12) side and an opposing surface (14) on the opposite side from the pocket inner surface (13). The base section (10) has: connection sections (10a, 10b) that connect the claws (11a, 11b) to the ring section (7) in the axial direction; and an intermediate section (10c) that connects the connecting sections (10a, 10b) to each other in the circumferential direction. The weld (W) is disposed in a