Abstract: Post-etching line width localities that occur due to resist film thickness localities can be corrected continuously, without the need for an expensive mask. After a resist applied to a thin film on a substrate is scanned and exposed by an exposure machine, which is selectively turned on and off by image data, the resist and the thin film are developed and etched to produce a pattern having a desired line width. Before the resist is exposed, a film thickness of the resist on the substrate is measured at each of plural locations on the substrate. The measured film thickness is reflected in a predetermined relationship between a pre-exposure film thickness of the resist and a post-etching corrective line width, for thereby determining a corrective line width amount at each of the plural locations on the substrate.