To more surely prevent meandering and slip.

Each pair of driving pulleys 28 and 29 and driven pulleys 46 and 47 having larger diameters than those of a driving shaft 25 and a driven shaft 45 is provided at a center part of the driving shaft 25 and the driven shaft 45. On both the sides, driving side auxiliary pulleys 30 and 31 and driven side auxiliary pulleys 48 and 49 having the same diameter as those of the pulleys 28, 29, 46 and 47 are mounted at prescribed intervals. The driven shaft side 45 is supported by a pair of arm members 40 and 41 and is energized in a direction separating from the driving shaft 25 by coil springs 35. A rib provided on an internal surface side of a carrier belt 50 is accepted between the driving pulleys 28 and 29 and between the driven pulleys 46 and 47 to be carried and driven.