The designing of an annular integral type is established by forming a cage of a resin material that satisfies the condition (a) that the ratio of its linear expansion coefficient to that of bearing steel is not more than 2 or the condition (b) that its water absorption percentage is not more than 0.5%, or both conditions (a) and (b), thereby preventing the occurrence of abnormal sounds by stabilizing the behavior of a segment type cage for an ultrathin-walled rolling bearing.
