A graph in which patterns are each regarded as nodes and nodes of patterns adjacent to each other at a first distance are connected with each other by an edge is produced, each of the patterns is classified into two types so that the two patterns corresponding to the nodes at both ends of the edge are types different to each other, a classification result is corrected by grouping the patterns in each node cluster connected by the edge or each node cluster connected via the node by the edge, and by inverting each of types of a pattern belonging to a same group as that of one pattern, out of a pair of patterns that are classified into a same type and that belong to respectively different groups adjacent to each other at a second distance, and a pattern layout diagram is created based on the corrected classification result.