Abstract: A drilling device comprises a drilling head including a rotating body through which runs a duct for supplying, under pressure, air, or mud, or water or other drilling fluid. At least one rotating cutting element is mounted on a shaft fixed on the rotating body so that the axes of rotation of the rotating body and of the cutting element diverge in the drilling direction. The cutting element is a disc having a ring-shaped cutting part. The rotating body bears on the opposite side to that bearing the rotating shaft of the disc a counter-reacting element placed in such a way that the element rests against the drilling wall to center the drilling head by compensating for the radial component of the reaction of the ground on the disc and to strengthen the wall. The point of contact of the element and wall which is highest up on the device is no higher than the highest point of the ring-shaped cutting part.