1. An exposure data generator for generating exposure data representing graphical information of a pattern to be exposed comprising a plurality of sides, comprising: a storage device for storing pre-correction exposure data which include information on positions and sizes of a plurality of patterns placed within an target region; a search device for classifying the plurality of patterns according to placement positions within the target region, searching for a first pattern which is adjacent to a side of a second pattern by using the classified patterns, and storing information on the first and second patterns to the storage device; a back-scattering intensity calculation device for calculating a back-scattering intensity from the plurality of patterns at an evaluation point on the second pattern; a movement quantity calculation device for calculating a movement quantity of the side of the second pattern when the side of the second pattern is moved, by using the information on the first and second patterns and the back-scattering intensity, so that a sum of a forward-scattering intensity from the first pattern, a forward-scattering intensity from the second pattern and the back-scattering intensity at the evaluation point becomes a reference exposure intensity; and a correction device for moving the side of the second pattern by the obtained movement quantity and correcting the information on the second pattern.