The invention relates to a locking device for fixing a lid (1) to the opening (8) of a pressure vessel, comprising at least two locking segments (5) that can be moved crosswise relative to the axis of the opening (8), said locking segments having projecting elements (6) and groove-shaped recesses in their periphery that in closed position cooperate with recesses (7) or projecting elements in the edge of the opening, wherein the displacement drive mechanism (4) of the segments (5) is hinged to the segments (5) and at least one site of action arranged on the lid (1) or on a component (3) that is connected to the lid (1). According to the invention, the segments (5) arranged in peripheral direction of the lid (1) are supported in an articulated manner on the lid (1) by means of a pivoting arm (16) that is separate from the displacement drive mechanism (4).