PURPOSE: To surely prevent a trolley from dropping, by arranging a pair of left and right side plates on which drop-preventing guide rollers adapted to roll on opposite sides of the lower flange of a rail of a trolley frame are shaft- supported, on opposite sides of a rail on which a running wheel rolls at the lower flange thereof.

CONSTITUTION: A trolley frame is constituted on opposite sides of a rail 3 having an I-like cross-sectional shape. Side plates 12, 12 coupled together at their center lower parts by means of a coupling shaft 14 are laid, drop- preventing guide rollers 7 each having a drop-preventing upper flange 6 are located in recesses 15 formed in the side plates 12 at both front and rear ends thereof, and are rotatably supported by vertical shafts 8 which are supported by upper and lower bearing fixtures 17, 9 fixed to the side plates 12 by means of bolts 16, 18. The lower bearing fixture 9 is formed so that its inner side plate is located in the vicinity of a lower extension line of the inner peripheral edge of the guide roller 7. Further, a pair of running wheels 2 provided with driven gears are pivoted on both front and rear sides of the intermediate part of the side plates 12, and are driven by a drive device.