To provide a method for forming fracture start sections of ductile metallic components by which neat fracture surfaces can be obtained, and an apparatus for forming the fracture start sections.

In the method for forming the fracture start sections of the ductile metallic components on the inner peripheral surfaces of through-holes of the ductile metallic components having the predetermined through-holes by irradiating the opposite positions of the inner peripheral surfaces of the through-holes with a laser beam and fabricating a number of recessed parts parted at a specified distance from the apertures on one side of the through-holes to the apertures on the other side at predetermined intervals, the inner peripheral surface of each through-hole is irradiated with the laser beam by defocusing the laser beam by the specified amount from the inner peripheral surface of the through-hole in place of irradiating the inner peripheral surface of the through-hole with the laser beam by exactly focusing the laser beam to the inner peripheral surface of the through-hole and simultaneously each recessed part is formed by supplying assist gas to the inner peripheral surface of the through-hole and while the inner peripheral surface of the through-hole is irradiated with the laser beam at a specified pulse, the laser beam is linearly moved from the aperture on one side of the inner peripheral surface of the through-hole to the aperture on the other side of the inner peripheral surface at a prescribed velocity.