[Problem] To achieve a structure that can reliably prevent the occurrence of creep between a pulley (2b) and an outer ring (7f). [Solution] The intersection angle (?) of the inside surfaces (23) on the two sides of each recessed part (17a) of the knurled pattern (19a) of the outer ring (7f) is 45° = (?) = 120° and the recessed parts are formed in a trapezoidal shape. The depth (h) of the recessed parts (17a) in the radial direction and the diameter (D) of a circle circumscribing the tip surface (22) of the protruding parts (18a) satisfy the relationship 0.004D = (h) = 0.015D and the length (L) of the bottom surface (21) of the recessed parts (17a) in the circumferential direction is kept within the range of 0.01D = (L) = 0.03D.
