An endless belt (11) to be provided on a driven pulley (4b) and a pulley rotation support apparatus for supporting the driven pulley (4b). In the pulley rotation support apparatus, there is used a three-point-contact-type or four-point-contact-type radial ball bearing (14b). An offset quantity .delta., which is an axial-direction distance between the center .alpha. of a radial load applied from the endless belt (11) to the driven pulley (4b) and the center position .beta. of the radial ball bearing (14b), is set 40% or less of the pitch circle diameter of the radial ball bearing (14b). The radial clearance of this radial ball bearing (14b) is set 0.2% or less of the above pitch circle diameter.