PURPOSE: To obtain a discoid tool which is excellent in abrasion resistance, by simultaneously radiating a beam of high energy density from 2 directions orthogonal to an angular part of a prescribed shape base material which is rotating, by a method for hardening said angular part by said beam.

CONSTITUTION: For instance, a slitting cutter 1 is rotated, and a laser beam 4 is separated into 2 directions of 4a and 4b through a transmission and reflection mirror 11. Subsequently, the beam 4a is radiated into the upper direction of a side 1b of the cutter 1. On the other hand, the beam 4b is simultaneously radiated toward the cutter edge part from the side of an end face 1c of the cutter 1 through a reflection mirror 12, etc. A surface-hardened layer obtained in this case becomes a layer having wide width on the face 1c, too, the edge part 1a is quenched extending over a wide area, and sufficient hardness is obtained. In this regard, after quenching of one side has ended, it is inverted, and the other side is quenched.