A boring tool capable of accurately forming a bored hole by securing the rigidity of a
reamer to prevent turnout of the
reamer at high speeds and enabling an increase in life by suppressing the breakage thereof by
cutting resistance. The boring tool (21) is inserted into a
pilot hole formed in a workpiece beforehand to
cut the inner wall surface of the
pilot hole. The boring tool comprises a shank part rotated about an axis (O), an edge part with a
cutting edge (30) at the tip of the shank part, and a
chip discharging groove (27) formed in the outer
peripheral part of the edge part and extending from the tip side to the rear end side. The
cutting edge (30) is formed at a crossed
ridge part between the wall surface (28) of the
chip discharging grove (27) facing forward in the tool rotating direction (T) and the outer
peripheral surface (29) of the edge part. The boring tool is characterized in that the cross-section of the
chip discharging groove (27) vertical to the axis (O) is formed in a U-shape.