The straightness and parallelism of a track surface on which rollers roll are measured within a range "L2" as a range for measuring the straightness and parallelism. The range "L2" is a range such that L2.gtoreq.0.8.times.L when a roller length is "L". When the dimension from the corner P of the flange on the inner diameter side to the starting point of the range "L2" is "L1", the dimension "L1" is ranged such that 0.8 mm.ltoreq.L1.ltoreq.2 mm. In this range, the straightness of the track surface of the outer ring in the axial direction is not more than 0.008 mm and the parallelism thereof is not more than 0.015 mm.