Abstract: A rotary rock drilling machine comprises a carriage having two ends, a rotary drilling drive arranged longitudinally displaceable on the carriage, a guiding head arranged on one end of the carriage, the guiding head and the rotary drilling drive defining a longitudinal axis of the machine, a drilling rod composed of a plurality of drilling rod parts which are releasably connected with one another, the drilling rod parts having a plurality of screw convolutions, the drilling rod parts having one end having a coupling pin with a snap pin and another end having a coupling bush with an engaging opening for the snap pin, a positioning device in the guiding head arranged to arrest a rotary position of the drilling rod, and an unlocking device for the snap pin, the positioning device including a locking bar which extends substantially parallel to the longitudinal axis and displaceable radially to the drilling rod, and which is insertable in at least one radial slot provided in the screw convolution of the drilling r