a low cost method and apparatus for simultaneous block melting of a material by laser enabling completion of work in a short time . a laser beam from a yag laser source etc . strikes a diffraction type optical element like a diffraction lens and is split into a large number of beams by diffraction and transmission . the beams are focused by a condensing lens etc . on a plastic surface as a large number of points or a line . the plastic is simultaneously heated to melt at these focused points for welding with another object or for removal . therefore , no deformation occurs in the worked material like in the prior art where a surface was scanned by a focused point . the worked material may be a metal etc . in addition to a plastic .