To make load for each cutter part the most suitable, discharge drill cuttings and improve performance of a drill tool by making the main cutter and the auxiliary cutter of a drill head specific shapes.

A rock drill 1 mounted on a rotation impact drill device is constituted so that a drill head 5 is fixed on the edge of a drill shaft having the discharge groove 3 of drill cuttings. A main cutter 6 and auxiliary cutters 7, 8 are arranged on the diameter of the intersection angle of 10-50 degrees on the drill head, the main cutter 6 is molded by a center area 9 and peripheral areas 10, 11 positioned at both the sides, and projected from the auxiliary cutters 7, 8 providing a cutting edge. In addition, a groove and a gap are provided among each cutter 6, 7, 8 to be connected to the discharge groove 3 of drill cuttings. Thereby the auxiliary cutters 7, 8 mainly have cutting function at the time of rotation, the main cutter 6 mainly has centering function at the time of rotation and impact, and the discharge performance of the drill cuttings is improved.