The invention relates to an impact device comprising a frame to which a tool is connectible, and between the frame and the tool a stress element (3) sup-ported to the frame of the impact device, and a hydraulic fluid space (6) and means for leading pressurized hydraulic fluid into and out of the hydraulic fluid space (6), respectively. The impact device comprises a rotatingly installed con-trol valve (5) having control channels (5b) for leading the hydraulic fluid inter-mittently from the hydraulic fluid space (6) to the return channel.