The present invention relates to a rock drilling device comprising a feed beam (4), which has a drill end (41) from which the drill point protrudes at drilling and a rear end (42) opposite said drill end. A rock drilling machine (5) is movable along the feed beam (4) and a pressure cylinder (6) is arranged at least partly inside the feed beam (4) with one end (622) movable relative to the feed beam (4) and one end (611) fixedly arranged relative to the feed beam. A feed line (51) is driven by the pressure cylinder (6) and connected to the drilling machine (5) for feeding it to and for along the feed beam (4). At least a part of the pressure cylinder (6) is arranged inside the feed beam (4) and the fixed end (611) of the pressure cylinder (6) is arranged at the rear end (42) of the feed beam, the pressure cylinder (6) being adapted to feed, via said feed line (51), the drilling machine (5) to and for along the feed beam. The invention also relates to a drill rig comprising said rock drilling device.