The invention concerns an arrangement for controlling a hydraulic rock drilling device. The adaptation includes a pressure ratio valve (18; 18') that is used for adjusting the relation between the pressures in the pressure channel leading to the percussion device and/or other actuator, such as a shank stabilizer (28), and the pressure channel leading to the feed mechanism. The pressure ratio valve (18; 18') is arranged to keep the relation between the pressures of the actuator and the feed mechanism constant over the normal drilling range.