To provide a method and a device capable of altering a curve of distribution of intensity of laser beam at a spot to be worked rapidly by a switching time up to submicrosecond.

In a method for generating a prescribed distribution of intensity of working laser beam 17 on the surface 19 of an object, at least one of a primary and secondary partial beams 3a, 3a", 3b, 3b', and 3b" each having a prescribed primary and secondary distribution of intensity is formed, and the output of each of the partial beams 3a, 3a", 3b, 3b', and 3b" is controlled and altered by a switching time up to submicrosecond. The partial beams 3a" and 3b" are then superposed so as to be a tertiary distribution of intensity and are directed onto the surface or the inside of the object 1 as a working beam 17, and attain a different action for a altered tertiary distribution of intensity of the working beam 17.