Drill body of indexable drill

A drill main body of an indexable drill disposed with a pair of first and second spiral flutes on a column-shaped outer circumferential surface with an inner blade tip cutting a hole center side mounted on a tip portion of the first spiral flute and an outer blade tip cutting a hole outer circumferential side mounted on a tip portion of the second spiral flute, the drill main body of an indexable drill discharging chips through the first spiral flute and the second spiral flute toward a shank while hole machining is performed with the inner blade tip and the outer blade tip,

• the drill being a deep hole machining drill having a length L of the first spiral flute and the second spiral flute equal to or greater than 4D relative to a drill diameter D that is an outer diameter of the outer blade tip,
• the first spiral flute being formed with a flute bottom diameter having a positive gradient such that the flute bottom diameter increases toward the shank, in axial direction, wherein the first spiral flute is formed with the flute bottom diameter having the positive gradient, and
• the second spiral flute being formed with a flute bottom diameter having a negative gradient such that the flute bottom diameter decreases toward the shank in axial direction.