PURPOSE: To enable forming a grinding guide mechanism of simple construction and less cost by projecting a pin from one of slide surfaces between a main body sleeve and an intermediate sleeve and providing the other slide surface with a pin guide groove for moving the intermediate sleeve by a predetermined grinding shift amount and moving in a grinding direction.

CONSTITUTION: When a motor for a grindstone 44 has been switched on and rotated, and a grinding handle 26 has been pushed along a guide groove 36 engraved on a guide plate 34, an intermediate sleeve 22 first moves concurrently by a length corresponding to the linear part 68 of a guide groove 28, due to the coupling of a pin 30 thereto. As the length of the linear part 68 is equal to the width of a contact plate 62, the tip of a drill cutting edge 14 comes in contact with the grindstone 44. Furthermore, the intermediate sleeve 22 when pushed turns and advances along a curved part 70 and can grind the drill cutting edge 14 by a predetermined amount. According to the aforesaid constitution, it becomes possible to carry out a predetermined grinding process simply by the easy operation for pushing the intermediate sleeve in a forward direction, and simple construction reduces cost.