PURPOSE: To partially prevent dirt from sticking to a blade by providing a washing water feeding device having a recessed groove which is provided in the radial direction with respect to a wafer cutting blade and a water introducing port for introducing washing water to said recessed groove, opposite to and close to the surface of said blade.

CONSTITUTION: A washing water feeding device 5 is fixedly provided close to the bottom surface of a blade 2 held between a chuck body 3 and a top ring 11, a recessed groove 6 for holding washing water is provided in a part opposite to the blade 2, and a water introducing port 7 through which water is externally fed, is connected to the recessed groove 6 via small ports 12. An entry prevention member 9 against any broken piece is provided in a direction in which the blade 2 advances toward the device 5. Water is always fully or overflowingly fed to the recessed groove 6. Thereby, even though a coolant liquid may flow only on the top surface of the blade 2, its bottom surface is always in contact with the washing water, which is adsorbed to the bottom surface of the blade due to negative pressure on the surface of the blade generated by its high speed rotation, and always flows on the surface of the blade due to centrifugal force, preventing dirt from sticking to the blade.