A laser beam machining method and a laser beam machining device capable of
cutting a work without producing a fusing and a cracking out of a
predetermined cutting line on the surface of the work, wherein a pulse
laser beam is radiated on the predetermined cut line on the surface of
the work under the conditions causing a multiple photon absorption and
with a condensed point aligned to the inside of the work, and a modified
area is formed inside the work along the predetermined determined cut
line by moving the condensed point along the predetermined cut line,
whereby the work can be cut with a rather small force by cracking the
work along the predetermined cut line starting from the modified area
and, because the pulse laser beam radiated is not almost absorbed onto
the surface of the work, the surface is not fused even if the modified
area is formed.