To effectively suppress chatter-vibration of cutting edges to improve the durability, and to improve the hole surface cutting accuracy.

Both tips 17, 18 fixed to the tip part 15 of a shank 12 are provided at symmetrical positions in diametrically opposite directions. Further, respective cutting edges 19, 20 of both the tips are provided with the first cutting edge parts 19a, 20a for cutting small diameter tapered surfaces on their tips, the second cutting edge parts 19b, 20b by which large taper angles can be formed in succession to the end edges of the respective first cutting edge parts, and the third cutting edge parts 19c, 20c which are provided at the end edges of the respective second cutting edge parts and which are used for cutting holes of the largest diameter larger than the diameter of the shank 12. Furthermore, an oil supply passage 25 consisting of a main passage part 26 and branch passages 27 to 28 for directly supplying cutting oil to the respective cutting edges 19, 20 and to the respective guide pads 21, 22 sides, is formed in the inside and in the axial direction of the shank.