PURPOSE: To smoothen the feeding of cooling fluid and to improve the life of a tool by inserting and fixing the narrow nozzle communicating with a cooling fluid-introducing hole into the hollow member which is connected to the joint of a tool body with sealing material and thrust bearing and is rotated in the tool for stone material, etc.

CONSTITUTION: The rear end of a hollow member 8 is inserted into the fitting hole 24a of the joint member 24 supported on a tool body 2 and is connected thereto with the sealing by O ring 48. The hollow member 8 is rotationally driven by a driving shaft interlocking with the driven shaft 38 by gears 36, 44, and a rotary drill 18 fitted to the hollow shaft 8 is rotated. A narrow nozzle 30 is fitted into the cooling fluid-introducing port 24b of the joint member 24 with its connected rear end, and the front end is fitted to the narrow nozzle 34 in the rotary drill 18. By this construction, mist M may be fed in axial direction in the hollow member 8 directly and smoothly by the narrow nozzle 30 from the introducing hole 24b.