PURPOSE: To reduce revolving power required for cutting, and to shorten the cutting time by setting the kinds, number, thickness size, etc., of a drill and a bit and cutting both internal and external peripheries of excavation while supplying sections among both internal and external peripheries and an article to be cut with a coolant.

CONSTITUTION: The diameter of a drill body 12 and the size and number, etc., of blades 14 are determined in response to the kind of an article to be cut, the scale of drilling, etc., and a binding material is added to the powder of diamond as the bits 14. Each bit 14 is arranged at intervals in the circumferential direction, and mounted on an end face 16 by brazing, etc. Each bit 14 has base sections 18 brought into contact with the end face 16 and front end sections 20 relative to the base sections 18 regarding the axial direction of the main body 12 at that time. The end faces of each base section 18 and each front end section 20 are formed in parallel with each end face 16 of the main body 12, and the end faces of the bit front end sections 20 are cut during a time when the bits 14 are rotated around the axis of the main body 12. The thickness size of the bits 14 is prescribed, annular clearances are formed among both internal and external circumferential surfaces 22, 24 relative in the radial direction of the main body 12 and the article to be cut, and the bits 14 are supplied with a coolant from the clearances.