A boring device including a main shaft which is rotated by a driving source 10 and includes an inner path 12a and an outer path 12b which has a double tube structure, wherein a drill 30 which has a venting hole 33 on a axial center extending from a shank 31b to the proximity of a blade 32 and hoods 17, 14which cover an outer periphery of the drill are provided at a front end of a double tube main shaft. An air-feeding mechanism 40 which supplies a compressed air to the inner path 12a and a dust collecting mechanism 50 which sucks an air in the outer path 12b are connected to a rear end of the double tube main shaft 12. A work piece is bored while the compressed air is supplied around a drill blade via the inner path 12a so that swarf generated is recovered to the dust collecting mechanism 50 via the outer path 12b.