A drill, comprising: a substantially columnar drill holder comprising, at a front end portion thereof, an inner insert pocket and an outer insert pocket formed closer to the outer periphery of the drill holder than the inner insert pocket; an inner cutting insert (1A, 1, 1',1") which is attached to the inner insert pocket and comprises a cutting edge; and an outer cutting insert (1B, 1, 1', 1") which is attached to the outer insert pocket and comprises a cutting edge, wherein the inner insert pocket is located passing through a central axis of rotation of the drill holder, and wherein each cutting insert comprises: an upper face and a side face, an intersection thereof forming the respective cutting edge, wherein the cutting edge of each insert includes a first cutting edge and a second cutting edge, wherein the inner cutting insert is mounted such that its first cutting edge protrudes from the front end of the drill holder in a side view, the outer cutting insert is mounted such that its second cutting edge protrudes from the front end of the drill holder in a side view, and the second cutting edge has a concave shape in a side view from said side face, and has a curved line (8, 9) at least along a part of the second cutting edge, wherein the second cutting edge of the cutting inserts comprises in said side view a first circular arc portion and a second circular arc portion located more remote from the central axis than the first circular arc portion, and a first radius of curvature of the first circular arc portion is smaller than a second radius of curvature of the second circular arc portion. a substantially columnar drill holder comprising, at a front end portion thereof, an inner insert pocket and an outer insert pocket formed closer to the outer periphery of the drill holder than the inner insert pocket; an inner cutting insert (1A, 1, 1',1") which is attached to the inner insert pocket and comprises a cutting edge; and an outer cutting insert (1B, 1, 1', 1") which is attached to the outer insert pocket and comprises a cutting edge, wherein the inner insert pocket is located passing through a central axis of rotation of the drill holder, and wherein each cutting insert comprises: an upper face and a side face, an intersection thereof forming the respective cutting edge, wherein the cutting edge of each insert includes a first cutting edge and a second cutting edge, wherein the inner cutting insert is mounted such that its first cutting edge protrudes from the front end of the drill holder in a side view, the outer cutting insert is mounted such that its second cutting edge protrudes from the front end of the drill holder in a side view, and the second cutting edge has a concave shape in a side view from said side face, and has a curved line (8, 9) at least along a part of the second cutting edge, wherein the second cutting edge of the cutting inserts comprises in said side view a first circular arc portion and a second circular arc portion located more remote from the central axis than the first circular arc portion, and a first radius of curvature of the first circular arc portion is smaller than a second radius of curvature of the second circular arc portion. an upper face and a side face, an intersection thereof forming the respective cutting edge, wherein the cutting edge of each insert includes a first cutting edge and a second cutting edge, wherein the inner cutting insert is mounted such that its first cutting edge protrudes from the front end of the drill holder in a side view, the outer cutting insert is mounted such that its second cutting edge protrudes from the front end of the drill holder in a side view, and the second cutting edge has a concave shape in a side view from said side face, and has a curved line (8, 9) at least along a part of the second cutting edge, wherein the second cutting edge of the cutting inserts comprises in said side view a first circular arc portion and a second circular arc portion located more remote from the central axis than the first circular arc portion, and a first radius of curvature of the first circular arc portion is smaller than a second radius of curvature of the second circular arc portion.