PURPOSE: To realize the stable cutting by improving the array of a throw-away tip in a throw-away type roughing end mill.

CONSTITUTION: Square throw-away tips 3 are fitted to a first twisted groove 1 at equal interval from the tip. The throw-away tips 3 are arranged in a second twisted groove 2 so as to compliment the clearance of the array, and throw-away tips 13 whose rotational loci are approximately superposed on the outer edge of the first throw-away tip 3a in the first spiral groove 1 are added to the tip side of the second throw-away tip 3c. As a result, the number of cutting edges at the tip part which are likely to be sooner damaged becomes doubled, and the cutting edges on the outer circumference are divided, obtaining the cutting where chips are excellently discharged and the vibration is suppressed.