A method for generating a pattern including patterns of cells having assist patterns arranged therein. The present invention provides a method for generating a pattern of a cell used when a mask pattern is generated by arranging cells selected from among a plurality of types of cells. The method includes generating a pattern including isolated rectangular pattern elements and an assist pattern as a cell pattern by obtaining data on a cell including the rectangular pattern elements and generating the assist pattern which assist resolution of the rectangular pattern elements in accordance with the data.