A locking device formed for arrangement in a venetian blind device, which has a plurality of lamellae (1, 1'), wherein each lamella (1, 1') has, on both sides, a respective lamella bracket (2, 2') parallel to a longitudinal axis of the lamella (1, 1') comprising sliding head (2a, 2a') and neck portion, and wherein the locking device has a profile rail, which - has an open longitudinal side and a plurality of recesses (12, 12') on one of the edges, which limit the open longitudinal side, and which - can be transferred between an unlocked position and a locked position by means of a rotational movement about a longitudinal axis of the profile rail, wherein - in the unlocked position, the neck portion of each lamella (1, 1') extends through the open longitudinal side and each lamella (1, 1') is movable along the profile rail, guided with the sliding head (2a, 2a') in the profile rail, and - in the locked position, the neck portion of each lamella (1, 1') is arranged in a respective one of the recesses (12, 12'), and each lamella (1, 1') is immovably arranged along the profile rail with the sliding head (2a, 2') in the profile rail in a position determined by the respective recess (12, 12'), wherein the locking device has an actuating element for triggering the rotational movement of the profile rail, which is preferably provided by an end portion of the profile rail on a first end or which is formed by a first journal end piece, which is connected in a rotationally fixed manner to the profile rail on a first end of the profile rail, characterised in that the end portion or the first journal end piece has a thread-like cam groove, - which adjoins the open longitudinal side of the profile rail and - extends in a circumferential direction corresponding to the arrangement of the recesses (12, 12') on the profile rail and - in which an actuating pin can be guided, which extends laterally from a bottom rail of the venetian blind device and which is movable in a positively driven manner on the bottom rail in a lamella plane, which is defined by the plurality of the lamellae (1, 1') and in which the longitudinal axes of the lamellae (1, 1') lie, so that the actuating pin guided in the cam groove triggers the rotational movement of the first journal end piece and thus of the profile rail. - has an open longitudinal side and a plurality of recesses (12, 12') on one of the edges, which limit the open longitudinal side, and which - can be transferred between an unlocked position and a locked position by means of a rotational movement about a longitudinal axis of the profile rail, wherein - in the unlocked position, the neck portion of each lamella (1, 1') extends through the open longitudinal side and each lamella (1, 1') is movable along the profile rail, guided with the sliding head (2a, 2a') in the profile rail, and - in the locked position, the neck portion of each lamella (1, 1') is arranged in a respective one of the recesses (12, 12'), and each lamella (1, 1') is immovably arranged along the profile rail with the sliding head (2a, 2') in the profile rail in a position determined by the respective recess (12, 12'), wherein the locking device has an actuating element for triggering the rotational movement of the profile rail, which is preferably provided by an end portion of the profile rail on a first end or which is formed by a first journal end piece, which is connected in a rotationally fixed manner to the profile rail on a first end of the profile rail, characterised in that the end portion or the first journal end piece has a thread-like cam groove, the locking device has an actuating element for triggering the rotational movement of the profile rail, which is preferably provided by an end portion of the profile rail on a first end or which is formed by a first journal end piece, which is connected in a rotationally fixed manner to the profile rail on a first end of the profile rail, characterised in that the end portion or the first journal end piece has a thread-like cam groove, - which adjoins the open longitudinal side of the profile rail and - extends in a circumferential direction corresponding to the arrangement of the recesses (12, 12') on the profile rail and - in which an actuating pin can be guided, which extends laterally from a bottom rail of the venetian blind device and which is movable in a positively driven manner on the bottom rail in a lamella plane, which is defined by the plurality of the lamellae (1, 1') and in which the longitudinal axes of the lamellae (1, 1') lie, so that the actuating pin guided in the cam groove triggers the rotational movement of the first journal end piece and thus of the profile rail.