PURPOSE: To prevent a chatter of a tool main body from occurring and improve the accuracy of a hole and the surface roughness by separating multiple cutting blades on the tool main body in the peripheral direction so that the corresponding portions are located in a range shorter than a half of the outer periphery of the tool main body.

CONSTITUTION: A tool main body 1 is a cylindrical body rotating around an axis O, and a raw tip 2 is brazed to its tip section. The solid tip 2 is made of a sintered hard alloy, and two cutting blades 3 are formed on the outer periphery apart by an angle θ (θ=90°) in the peripheral direction. The angle θis preferably set in a range of about 45W175°. A guide 4 extending in the axis O direction along the rotating locus of the cutting blade 3 is formed on the wall section facing the opposite side to the cutting blade 3. This guide 4 has a diameter almost equal to the diameter of the cutting blade 3 and is brought into sliding contact with the inner wall of a hole to prevent the deflection of the tool main body 1.