A boom arrangement (7) for a rock drill rig (5) including a feed beam unit (8) for displaceable reception of at least one rock drilling machine (10, 10′), a support unit (13) for connection to and support of a rotator unit (12), a boom unit (11) between the rotator unit (12) and the feed beam unit (8) for displacement of the feed beam unit in planes essentially at right angle to a main plane (P) for the support unit (13), wherein the rotator unit (12) is arranged for rotating the feed beam unit (8) around an axis (A), which is essentially-perpendicular to said main plane (P), wherein the support unit (13) is connectable to a vehicle unit being part of the rock drill rig (5), and being arranged for displacing the rock drill rig. The support unit (13) has joint connecting elements (14) being sidewardly connectable for connection to a sidewardly directed carrier device (15, 17) which is attachable to the vehicle unit, and a lower abutment side (16) for lying supporting against an outer substrate. The invention also concerns a rock drill rig.