Abstract: A locking device at a trailer coupling, including a first part (1), which is adapted to be attachable to a towing vehicle, and a second part (2), which is adapted to be coupled to a trailed vehicle and to be releasably attachable to the first part (1). The first part (1) includes an opening (8), into which the second part (2) is introducable, and a locking bolt (10), which is displaceable in its axial direction into the opening (8) in the first part (1) to lock the second part (2) by engagement in a locking recess (11) therein in the position thereof where it is introduced in the opening (8) of the first part (1). The locking bolt (10) is urged by a spring (20) in a direction towards the opening (8) in the first part and manually operable in the opposite direction.