A hollow cylindrical pulley body 5 is carried rotatably by a hollow cylindrical shaft member 11. A support rod 8 is inserted in the shaft member 11, and the shaft member 11 is elastically supported to the support rod 8 through an elastic body 10. The elastic body 10 is provided within a quarter of the periphery of the support rod 8 that is located, when viewed along the axis of the shaft member 11, forward of the line of action of a radial shaft load on the shaft member 11 with respect to the direction of rotation of the pulley body 5. With this configuration, when the drive belt 3 deviates to one side, the pulley body 5 is immediately angularly moved so that it is inclined with a level difference with respect to the direction of the radial shaft load and is positioned obliquely relative to the drive belt 3. In this manner, a force of compensating for the deviation of the drive belt 3 is produced to avoid its wobbling.