PURPOSE: To evade leaking of granular substance and to eliminate opening and closing operation of gates by automatically actuating stoppers which are attached to respective side gates by means of a link in such a manner that said stoppers are locked to the gates when they are fell down while undone therefrom when they are tilted.

CONSTITUTION: A fixed stopper 11 and a stopper 12 which advances or retracts toward or from a gate 7 are attached to a side gate 10. The stopper 12 is urged by a spring 13 in the direction of the gate 7 and has a hole 14 at the center. A small diameter part 29 and a tapered part 30 of a shaft 15 are inserted through the hole 14 and as the shaft 15 is moved upward, the tapered part 30 forces the stopper 12 to retract from the gate 7. The shaft 15 linked to a lever 20 via a lever 18 and a rod 19 is moved up by the force of a spring 25. One end of the lever 20 is engaged with a bracket 2 which is fit to a frame 1 so as to force the shaft to a high position when a deck 2 is fell down while detached from the bracket 2 so as to allow upward motion of the shaft 15 when the deck 2 is tilted.