a double articulating hook lifting apparatus usable mounted upon a truck or trailer for loading and unloading containers with respect thereto and also being usable for dumping the containers . the locking mechanism operates to secure a movable arm to the pivot frame 2 to stop pivotal movement relative to one another , which also facilitates the movement required for dumping of the contents of the container while mounted on the vehicle . the locking device is automatically allowed to move to the locked position by the movement of the jib away from the arm , preferably in a telescoping manner . this movement occurs as the last step in the sequence of container loading to thereby automatically provide locking between the arm and the pivot frame 2 to prevent pivotal relative movement therebetween whenever the container is in the loaded position or is in dumping mode . as the container unloading sequence is initiated the jib moves toward the arm or telescopingly thereinto which powers unlocking of the locking mechanism as the first step in the sequence of container unloading .