PURPOSE: To prevent movement of a cargo in the opposite direction during drawing work by providing first and second reciprocating slats through a fixing slat, respectively connecting them to a driving means, making it possible to simultaneously drive both of the slats in the carrying direction and constituting it free to draw the other at the time when one of them stops.

CONSTITUTION: First and second slats 16, 18 are juxtaposed in the longitudinal direction with a fixing slat 14 between them, respectively connected by cross direction connection driving beams 38, 42, connected to respective hydraulic cylinders 44, 46 by slat connectors 36, 40 and independently driven. Additionally, both of the slats 16, 18 are devised free to simultaneously move in the carrying direction of a cargo and free to draw in the opposite direction at the time when the other slat is in a stationary state. Consequently, at the time of drawing, the cargo is supported by the slat in a stationary state and the fixing slat 14. In this constitution, it is possible to prevent movement of the cargo in the opposite direction at the time of drawing.