PURPOSE: To let coolant function as both coolant and lubricant with coolant successfully supplied to a cutting tool in such a way that no discharge pressure is lowered under the influence of centrifugal force even at the time of high speed revolution.

CONSTITUTION: A push rod 13 is connected to the inner end section of a tool holder 10 while being penetrated through a spindle 9, and a coolant feed path 15 is bored therein in the axial direction. The tip end section of the spindle 9 is formed into a cylinder section 17 in the axial direction so as to be coupled in a piston 19 provided with a coolant port 18. An oil feed port 12a is bored in the tool holder 10 while being inclined to its axial direction in such way as to be communicated with the coolant port 18. A communication hole 21 is bored between the cylinder section 17 and the coolant feed path 15 in such a way that the piston 19 is pushed in, and sealant 22 is applied to the end face of the piston 19 in such a way that the periphery of the oil feed port 12a is sealed.