The invention concerns an apparatus comprising a body (2) wherein a piston (6) is mounted sliding alternately driven by an incompressible fluid under pressure, said body containing part of a tool (4) which is guided in translation in a wear sleeve (3), the end of the tool located inside the body being subjected to the repeated impacts of the piston (6), while the other end projects beyond the body and is designed to be supported on the rock or analogue to be destroyed, the tool being retained in the body by at least a transverse key (13). One of the keys (13) retaining the tool passes through aligned holes provided in the body (2), into the wear sleeve (3), and overlaps inside the inner cylindrical space of the sleeve, the tool (4) having a transverse groove (12) for the key (13) to pass through.