To provide a ball bearing which is capable of sufficiently ensuring the durable service life a ball even under a service condition where foreign matters intrude into the bearing and the temperature rise is high.

A steel in which the content of Si and Mn is increased, is used for a material of a ball 3, and the balls are carbonitrided, and hardened so that the retained austenite in a carbonitrided layer 3a formed on a surface layer part of the balls 3 is 20-50 vol.%. Generation of the surface separation attributable to generation and propagation of cracks is suppressed, and the durable service life of a ball bearing is remarkably improved even under a service condition where foreign matters intrude into the bearing and the heat generation is large at a bearing part.