A generation method of a light intensity distribution uses a first light modulation element and a second light modulation element which are arranged to be apart from each other by a distance D and face each other in parallel to optically modulate a light beam which enters the light modulation elements, thereby generating a light intensity distribution on a target surface. The first light modulation element has a pattern formed by repeating a basic unit having a pitch P. The distance D is set to a distance with which the light intensity distribution generated on the predetermined surface is not changed even if a relative position of the first light modulation element and the second light modulation element is shifted in a plane direction.