A drill in which a cut debris discharge groove is formed at an outer periphery of a front end section of a drill body rotated about an axis and a cutting edge is formed at a front end of the drill body, wherein a wall surface of the cut debris discharge groove, which faces forward in a rotational direction of the drill, is formed to have a concave curve line shape extending in a cross-section perpendicular to the axis, the concave curve line shape extending along a first circular arc, wherein a margin section is formed at an intersecting ridgeline section intersecting the wall surface and an outer peripheral surface of the front end section of the drill body, and wherein the margin section is located on a cylindrical surface having an external diameter equal to the external diameter of the cutting edge and having the axis as a center, wherein an intersection ridgeline between the margin section and the wall surface is formed as a leading edge of the front end section of the drill body, wherein a bottom surface of the cut debris discharge groove, which continues to the wall surface and which faces an outer peripheral side of the drill body, is formed to have a concave curve line shape in the cross-section perpendicular to the axis, the concave curve line shape extending along a second circular arc to be tangent with a core diameter circle at the front end section of the drill body, wherein the first circular arc has a greater radius than the second circular arc and is in contact with the second circular arc at a position closer to the leading edge side than the point of contact between the second circular arc and the core diameter circle, characterised in that in the cross-section perpendicular to the axis, the position at which the first circular arc is in contact with the second circular arc is located in front of a line segment joining the leading edge and the axis in the rotational direction, wherein in the cross-section perpendicular to the axis, the point of contact between the first and second circular arcs is within a range of 0.1 x D to 0.35 x D with respect to the external diameter D of the cutting edge from the axis, wherein with respect to the external diameter D of the cutting edge, the radius of the first circular arc is within a range of 1.0 x D to 3.0 x D, and the radius of the second circular arc is within a range of 0.2 x D to 0.4 x D, and wherein in the cross-section perpendicular to the axis, a groove angle between the first radius line that passes through the axis and is in contact with the first circular arc and the second radius line that is in contact with the second circular arc, is within a range of 60° to 90°. wherein a wall surface of the cut debris discharge groove, which faces forward in a rotational direction of the drill, is formed to have a concave curve line shape extending in a cross-section perpendicular to the axis, the concave curve line shape extending along a first circular arc, wherein a margin section is formed at an intersecting ridgeline section intersecting the wall surface and an outer peripheral surface of the front end section of the drill body, and wherein the margin section is located on a cylindrical surface having an external diameter equal to the external diameter of the cutting edge and having the axis as a center, wherein an intersection ridgeline between the margin section and the wall surface is formed as a leading edge of the front end section of the drill body, wherein a bottom surface of the cut debris discharge groove, which continues to the wall surface and which faces an outer peripheral side of the drill body, is formed to have a concave curve line shape in the cross-section perpendicular to the axis, the concave curve line shape extending along a second circular arc to be tangent with a core diameter circle at the front end section of the drill body, wherein the first circular arc has a greater radius than the second circular arc and is in contact with the second circular arc at a position closer to the leading edge side than the point of contact between the second circular arc and the core diameter circle, characterised in that in the cross-section perpendicular to the axis, the position at which the first circular arc is in contact with the second circular arc is located in front of a line segment joining the leading edge and the axis in the rotational direction, wherein in the cross-section perpendicular to the axis, the point of contact between the first and second circular arcs is within a range of 0.1 x D to 0.35 x D with respect to the external diameter D of the cutting edge from the axis, wherein with respect to the external diameter D of the cutting edge, the radius of the first circular arc is within a range of 1.0 x D to 3.0 x D, and the radius of the second circular arc is within a range of 0.2 x D to 0.4 x D, and wherein in the cross-section perpendicular to the axis, a groove angle between the first radius line that passes through the axis and is in contact with the first circular arc and the second radius line that is in contact with the second circular arc, is within a range of 60° to 90°.