Drilling system

The invention concerns a drilling system having a drilling head (2, 2') fixed to a drill string (3) which comprises an outer pipe (12, 12') and a percussion string (13, 13') inserted therein, wherein the percussion string (13, 13') comprises a plurality of rods (14, 14') which bear against each other with their end faces (19, 20; 19', 20'). One object of the present invention is to provide a drilling system with an inner percussion string, which permits a greater variation in the drilling direction and which can be used as a directional drilling system. To attain that object the outer pipe (12) is adapted to be deformable along its longitudinal axis and the end faces (19, 20) which bear against each other of two rods (14) are so designed that they bear against each other substantially in surface contact upon inclined positioning of the axes of the two rods (14) relative to each other.