PURPOSE: To prevent occurrence of clog with splash by furnishing a cap at the tip of a tool body in such a way as enclosing the discharge hole while the opening of the cap is directed to the base end in the axial direction, putting the inside space of this cap in communication with a splash exhaust groove, and thereby promoting smooth exhaust of the splash even in case the prepara tory hole to undergo the intended processing is long.

CONSTITUTION: Machining oil L spouted out of a discharge hole 9 via an oil hole 8 in a tool body 1 from the machine tool side when the machining process is executed, is once supplied to the space C in a cap 11, and a great major portion of the supplied oil inverts its flowing direction and is spouted from an opening at the base end of the cap 11 toward the base end in the axial O-direction. Because this opening on the base end side is leading to splash exhaust grooves 6 in cutting edge chips 3, the machining oil L supplied to the tool body 1, as a result, flows into the exhaust grooves 6 from the foremost part so that a flow directed from the foremost in the axial O-direction to the base end is generated in these grooves 6. Accordingly the splash in the grooves 6 can be exhausted smoothly owing to the flow of machining oil L.