PURPOSE: To provide a long service life by cooling a grinding wheel which grinds building materials such as cement boards, gypsum boards and concrete boards, ceramics, glass, alloy and the like.

CONSTITUTION: A cylindrical shell 12 where abrasive grains are electrically- deposited onto an outer peripheral surface and both ends are closed is supported so as to rotate. A cooling fluid feed/discharge pipe 13 is mounted onto a shell 12. A cooling liquid jetting pipe 17 for jetting cooling fluid to the inside of a grinding wheel body 12 is mounted inside the cooling fluid feed/discharge pipe 13. A feed pipe 15 for feeding cooling fluid and the cooling fluid feed/ discharge pipe 13 in the shell 12 are connected with each other through a rotary joint 14. A discharge pipe 16 for discharging cooling fluid passing through the grinding wheel body 12 is connected to the rotary joint 14.