A radial ball bearing 14 of the three point contact type or four point contact type is used for the rolling bearing for a compressor pulley. The offset amount &dgr;, that is the axial distance between the center &agr; of the radial load applied to the follower pulley 4 from the endless belt 11, and the center &bgr; of the radial ball bearing 14 is 40% or less of the diameter of the pitch circle. In addition, the radial clearance of the radial ball bearing 14 is 0.2% or less of the diameter of the pitch circle. With this construction, the durability of the rolling bearing to support the follower pulley 4 is secured while made compact.