The present invention discloses a locking device having a control unit with a first control element with a first surface (O1) and a second control element with a second surface (O2), the two control elements being moveable relative to each other with their two surfaces, a spatial region (intermediate space Z) which is filled at least partially with a magnetorheological and/or electrorheological material (M) and is disposed between the first and the second surface, and a field producer (4) with which a magnetic and/or electrical field can be produced in at least a partial region of the material-filled part of the intermediate space, a locking unit with a piston unit (2) and a locking system (3) with which the piston unit can be locked, the two control elements being able to be coupled to each other by the field produced in the intermediate space and the locking state of locking system and piston unit being able to be changed by means of this coupling.