PURPOSE: To improve a drilling work by forming a flushing passage connecting with each drilled portion in an eccentric rock drilling tool at the tip of a guide member rotating in a casing tube.

CONSTITUTION: A drilling tool is provided that rotates and drives a guide member 10 for holding an eccentric bit 22 and a pilot bit 23 in a casing tube 11. Flushing medium passages 62, 63 are respectively provided for the member 10 and a shaft 21, and are branched to openings 64, 65, 68, 69 and longitudinal grooves 66, 67. The member 10 is provided with flushing grooves 70, 71 and an ejector opening 72 connecting to a passage 16. The flushing medium is made to flow from the front surface of the bit 22 to the groove 70 through a notch 73 and a shoulder portion 33, and a part of the medium is made to flow from a guide groove 74 to the groove 70. Mixture of the flushing medium and a drilled matter is made to flow out from the groove 71. Thus, heavy clay soil can be drilled effectively.