A drill string guide device (1) for mounting to a feed beam of a rock drill rig and for the support of a drill string (38) , including a housing (6) wherein is arranged a piston cylinder device for maneuvering of a first jaw (7) and a second jaw (8) , wherein each one of the jaws is movable between an engagement position in the direction towards a position of the drill string (38) , for engagement therewith, and a releasing position in the direction from the position of the drill string (38) for releasing thereof . The piston cylinder device includes a first fluid cylinder (13) with a first piston unit (9) for maneuvering of the first jaw, wherein the first jaw is supported by the first piston unit, and the piston cylinder device includes a second fluid cylinder (35) with a second piston unit (14) for maneuvering of the second jaw, wherein the second jaw is supported by the second piston unit, which is guided in the first piston unit. The invention also concerns a rock drilling device.