To carry out rough working being a prepared hole working with one tool, and to further improve roundness of a hole formed on a workpiece.

This rotary cutting tool for drilling satisfies all following conditions: (1) a body has a flute part the helix angle of which is 5 to 30 degrees; (2) a polycrystal diamond chip 4 is arranged as a slant blade on a margin part so as to run along it within a range of 0.2 mm; (3) a preceding blade part 6 is formed on the front side in the tool proceeding direction and a finishing blade part 7 is integrally formed on the rear side of the polycrystal diamond chip; and (4) central height H of blade chamfer parts 9, 11 is 00.2 mm. The tool also has capacity to roughly work as it can continuously work but not intermittently work though it is one piece of the tool, improves discharging efficiency of chips by lowering discharging resistance of the chips while parting the chips, thereby eliminates influence of the chips as much as possible in cutting, and further improves the roundness of the hole formed on the work.