Abstract: The anti-theft device comprises essentially a movable vertical plate extending through an opening formed in the rain-strap overlying the doors of the container; this plate is adapted to drop by gravity to a position in which it is located behind lug extensions of the upper ends of the lock rods associated with each door panel to prevent the opening movement of the rods as long as the movable plate is not raised to a position overlying the lugs, this movable plate being rigid with a horizontal cover plate disposed on top of the container and prevented from being raised to a height sufficient for releasing the rods by another stacked container.