ROCK DRILLING DEVICE

A method of monitoring a rock drilling and a rock drilling device. The method comprises generating a stress wave which propagates in a tool (9) of the rock drilling device, measuring the stress wave propagating in the tool and measuring a drilling parameter indicating a drilling penetration rate (DPR). The method further comprises identifying, from the measured stress wave propagating in the tool, at least one of a compressive stress wave and a tensile stress wave of a reflected stress wave reflected from a rock (12) to be drilled back to the tool, determining at least one property of the at least one of the compressive stress wave and the tensile stress wave of the reflected stress wave, detecting, on the basis of a change in the at least one property of the at least one of the compressive stress wave and the tensile stress wave, that the tool is approaching the cavity (16).