Abstract: The rock drill apparatus (1) comprises a rock drill machine (6) provided with a percussion device (4), a feed device (9) and a tool (7), the tool (7) end comprising a bit (8) for breaking rock. The tool (7) is arranged to transmit impact energy generated by the percussion device (4) as a compression stress wave to the bit. The feed device (9) is arranged to thrust the tool (7) and the bit (8) against the rock to be drilled, whereby on drilling at least part of the compression stress wave generated by the percussion device (4) to the tool (7) reflects from the rock to be drilled back to the tool (7) as tensile stress, and impact energy of the percussion device (4) is adjusted on the basis of the level of tensile stress (?v) reflecting from the rock.