PURPOSE: To effectively prevent oscillation by parallely arranging two belt which are spaced spaced apart and driven in the sme direction, as driving means, and selecting the space between the belts so as to frictionally connect the belts to a carrior.

CONSTITUTION: Belt tensioners 15, 16 have tapered portions 15a, 15b; 16a, 16b on their longitudinal both ends. Continuous space reduction between belts is secured in inward direction of a driving device 1. Margin between belts 13, 14 and running rollers 4, 5 of a carrior 3 is gradually decreased on inlet and outlet of the driving device 1. The belts 13, 14 are pressed against the rollers 4, 5 or a running roller support body 20. The carrior 3 is transfered through a sub-lane by the vibration of a driving chain 8. A driving motor 11 is started immediately before the carrior 3 runs into the driving device 1, so that slight sliding friction occurs between the support body of the carrior 3 and belt tensioning sides 13a, 14a.