To prevent a harmful effect on the health of a worker due to inhaling of vapor of cutting oil and to remarkably reduce load on the environment by removing heat generated in cutting work from the tool side, not from the outside to thereby remarkably reduce the quantity of cutting oil used mainly used for cooling.

A passage 2d is provided in the inside of a part 2 required to be cooled in a tool 2, a liquid as a cooling medium is passed through the passage 2d, and the liquid passed through the passage 2d to raise its temperature is cooled by a heat exchanger, and circulated through the passage 2d to remove heat from the tool 2.