To perform opening and closing operation remotely without needing the direct manual work of a worker.

A dislocation preventing jig 21 to prevent a fall of a suspending cargo comprises an energizing member 32 energized in a hook closing direction; a pull string 3 pulled out from the dislocation preventing jig 21 and moving the dislocation preventing jig 21 through opening and closing of the hook 2; a stopper member 31 arranged in the middle of the pull string 3; a cylinder body 4 to slidably contain the stopper member 31; a stopper lock member 41 disposed in the middle of the interior of the cylinder body 4 and in a position wherein the stopper member 31 is locked when the pull string 3 is pulled until the hook 2 is released; and a reaction force member 42 arranged in the cylinder body 4 located closer to the pulling direction side of the pull string 3 than the stopper lock member 41 and applying a reaction force in a direction in which the stopper member 31 is separated away from the stopper lock member 41.