The locking device (1) for locking a first element relative to a second element comprises : - one locking element (8) provided on the first element, movable in a first direction (F) between an inactive position and an active position; - a biasing element (20) for urging the locking element (8) towards its inactive position, - one complementary locking element (10) provided on the second element, arranged to move the locking element (8) from its active position to its inactive position and retaining the locking element (8) in its inactive position. The locking element (8) is further movable in a second direction (D) between a locking position and an unlocking position, wherein the locking element (8) is moved away from the complementary locking element (10).