of the paired flange portions in this embodiment in order to effect such restriction when the thickness of the convex portion 34 in the axial direction is denoted by a the distance between the step surface 33 and the end surface of the clutch inner race 21 is by b and the distance between the both end surfaces of the clutch retainer 28 a and the inner side surfaces of the flange portions 27 a 27 b is by c respectively the values for a to c are set to satisfy the relation c gt b u2212 a taking an error in assembly and the assembling performance into consideration for instance when a difference b u2212 a is 0 to 0 5 mm the distance c is set to be larger than 0 05 mm note that the step surface 33 and the end surface of the clutch inner race 21 are the portions rotating together with the clutch retainer 28 a for this reason when a side surface of the convex portion 34 and the step surface 33 or one of the end surfaces of the clutch inner race 21 are brought into contact as described above and the roller clutch 10 is overrun the contact portions of the both surfaces do not rub each other moreover if the dimensions and the positional relations of the respective parts can be strictly regulated without considering an error in assembly the object of the present invention can be attained by satisfying the relation c gt b u2212 a 2 in this case however it should be arranged such that the distances c between the clutch retainer 28 a and the flange portions 27 a 27 b are equal to each other in a state.