Abstract: A drilling apparatus has a rotatable drilling rod (15) on the leading end of which is mounted a bit assembly including a bit (10) and a bit driver (12) for reciprocating the bit. The bit driver is powered by a high pressure fluid supplied from a fluid pressurizing apparatus interposed between the rod and bit assembly and including a device (16,18/114) for raising the pressure of fluid in a closed circuit into which said bit driver is connected, the said device being driven from a power source remote from it, for example, on the surface of the ground in which a hole is being drilled.