A locking device (10) is serving for, with a lock (18), locking an already closed door (4) which is mounted with hinges (6) on a frame (5) in a gable (3) of a container (1). The door is held in the closed position by a turnable locking bar (7) which, at least at one end, has a projection for, by turning the bar, engaging it with a holder on the frame. The locking device (10) furthermore comprises a lock hole (25) running through the locking bar (7), the lock hole (25) assumes, in the closed position, a direction mainly parallel to the door plane; a house (11) with a channel (12) attached to the door, the channel (12) encloses the locking bar (7), and a bolt guide (22) which is in alignment with the lock hole (25) in the closed position; and a sliding bolt (23) for sliding through the bolt guide (22) and the lock hole (25) and locking the locking device (10) by means of locking means (37) which engage with tumblers (27) in the lock (18). A combination lock can advantageously be used as lock. The locking device provides a better guarantee against burglary than known so far and spares you the trouble of keys if the lock is a combination lock.