A locking device for locking a leaf of a leaf installation has first and second locking elements with respective first and latching elements. The second latching element is located at an end facing the first latching element and capable of a latching operative engagement with the first latching element. The second locking element is stationarily disposed relative to the leaf installation. The first locking element is disposed with regard to the leaf to move correspondingly to a movement of the leaf, so that the first locking element is moved translationally into a locking position towards the second locking element and away from the second locking element into an unlocking position. One of the locking elements has an activating element operable to allow for the latching operative engagement between the latching elements in a blocking position and to prevent the latching operative engagement in a release position.