To remarkably decrease possibility of that a drill head is restricted by reinforcing iron bars regardless of diameter of the drill head even when drilling work is applied on an reinforced concrete.

At least three pieces of cutters 7-9 made of a rigid alloy are provided on a drill head and these cutters are arranged on the outer periphery of the drill head 5 in such an arrangement that they are at least partly close to a guide region 14 connected with the axial direction of the drill head 5. At least two mutually adjoining cutters positioned on the outer periphery of the drill head 5 forms each other an angle β of approximately 100°-approximately 150° and are mutually divided by at least one head waste channel 10-12 in the outer peripheral direction and the head waste channel is connected with at least one discharge channel provided spirally on a shaft 2.