Abstract: A lock device for a hinged cargo door of a truck trailer has a housing with a vertically extended groove in one side wall for receiving the rotatable cargo door lock bar. A transversely extended lock pin in the housing is transversely movable through an opening in the same side wall for insertion into a registered hole in the cargo door lock bar in the locked position thereof. Transverse movement of the lock pin is controlled by a simple lock mechanism including a key operated lock shaft having a rocker arm rotatable therewith and having a free end connected to the lock pin for transverse movement of the lock pin in response to rotation of the lock shaft.