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 .