1. A SELF-PROPELLED DRILLING MACHINE COMPRISING, IN COMBINATION, A RIGID HOUSING; A RADIAL GUIDE BEARING AT THE FRONT END OF SAID HOUSING; A DRILLING TOOL ROTATABLY MOUNTED IN SAID RADIAL GUIDE BEARING AND OF A SIZE SUITABLE TO BORE A HOLE INTO WHICH SAID HOUSING CAN PASS; A DRIVING MECHANISM IN SAID HOUSING AND COUPLED TO SAID DRILLING TOOL FOR DRIVING THE SAME; AN ADVANCING MECHANISM DISPOSED IN SAID HOUSING FOR ADVANCING THE MACHINE IN THE BORE HOLE AND COMPRISING ROLLERS DISPOED ON THE PERIPHERY OF SAID HOUSING, SHAFTS TRANSVERSELY MOUNTED IN SAID HOUSING AND EACH CARRYING A PAIR OF SAID ROLLERS RESPECTIVELY ON OPPOSITE END PORTIONS OF SAID SHAFTS, STEEPPITCH SCREW THREADS FORMED AT SAID END PORTIONS OF SAID SHAFTS AND IN ENGAGEMENT WITH CORRESPONDING STEEP-PITCH SCREW THREADS FORMED IN BORES OF SAID ROLLERS SPRINGS ACTING ON SAID ROLLERS FOR URGING THE SAME OUTWARDLY, AND GEAR MEANS COUPLING SAID ROLLERS TO SAID DRIVING MECHANISM; AND A GUIDE DEVICE AT HE REAR OF SAID HOUSING FOR GUIDING SAID HOUSING IN SAID BORE HOLE.