SMALL-DIAMETER DRILL

PROBLEM TO BE SOLVED: To improve a small-diameter drill to suppress a decrease in strength of a cutting edge outer peripheral part without providing a return part while sufficiently securing sharpness of the cutting edge outer peripheral part, and to obtain excellent processing precision and excellent abatement processability.SOLUTION: A small-diameter drill of 3 mm or less in diameter which has a tip cross-thinned has a flute part cutting edge 4a curved in a concave shape so that an amount "d" of concave from a virtual straight line SL connecting a radially outer end P of the flute part cutting edge and a radially outer end Q of a thinning part cutting edge to each other is 0.5-2% of a drill diameter D in front view. The ratio of a length B of the thinning part cutting edge and a length A of the flute part cutting edge is set to (0.6 to 0.9):1, and a radius R1 of curvature of a heel-side groove surface of a flute is made smaller than a radius R2 of curvature of a flute part cutting edge-side groove surface.