PURPOSE: To enable to grind with high accuracy, by a method wherein temperature rise is suppressed by passing a coolant to a grinding wheel head part, and the head part is prevented from thermal stress deformation by causing the coolant to flow to the work and a head part of the grinder.

CONSTITUTION: The coolant fed under pressure from a coolant tank 1 flows to a lower part of the grinding wheel head part 7 through a passage A, flows upward through the internal space of a grinding wheel head frame 9, and flows downward to an upper part of a work head 10 through a coolant nozzle 8' to cool the work. Then, the coolant flows on the head 12 as indicated by arrows C, D, E, F, is coolected into a liquid-collecting groove 13, and is returned into the tank 1. In the grinding wheel head part 7, the flowing coolant envelops a grinding wheel spindle 5 and a motor 6, fills up a hollow part and flows upwards, the heat generated at a bearing fitted into the wheel head frame 9 and the interior of the motor 6 is transmitted to the coolant through convection. The coolant having acted for preventing temperature rise cools the work, and equalize the temperatures of the work head 10 and the head 12.