To permit stable travel on branch paths by means of a simple arrangement and to prevent lateral slip.

In travel rollers 26 mounted at both the front and rear of a truck 23, the front left travel roller 26 and the rear left travel roller 26 pass through a clearance 22b in a conveying rail 22 in sequence and are then derailed when traveling to a branch path of conveyance, but even if one of the travel rollers is derailed, other travel rollers 26 sandwich a travel part 22a from above and below, thus enabling the truck 23 to continue to travel without tilting and to smoothly and stably travel along the branch path of conveyance. As a result, the need to use a lateral slip prevention mechanism is eliminated and stable travel at high speed is made possible.