1. A method for inspecting plate patterns which are formed by exposure using exposure data patterns having a plurality of patterns, the method comprising: a fine patterns removal processing of forming reference data patterns by performing, to a plurality of patterns included in the exposure data patterns, a logical sum processing of changing a plurality of overlapped patterns into a single pattern; a minus-sizing processing of fining a side of the patterns in a first width; and a plus-sizing processing of thickening the side of the patterns in the first width; and a pattern inspection processing of comparing the plate patterns with the reference data patterns and detecting disagreement of both the patterns as defective patterns.