1. A pattern noise removal device which removes a background pattern noise having periodicity from a digital image, comprising: a candidate pixel extracting module which extracts candidate pixels that constitute the background pattern noise from pixels within the image based on density of each of the pixels; a dot pattern feature extracting module which extracts a feature of a dot pattern formed by each of the candidate pixels and peripheral neighborhood pixels among the extracted candidate pixels; a dot pattern area extracting module which extracts a dot pattern area including the periodic candidate pixels and neighborhood pixels having the feature of the dot pattern; and a periodic pattern noise removal module which removes the periodic candidate pixels and neighborhood pixels included in the dot pattern area as the background pattern noise.