In an exposure step, a combination of a first photomask and a second mask is used. The first mask has a real pattern corresponding to the pattern actually formed on the film to be processed, and a dummy pattern added for controlling pattern pitch in the first photomask within a prescribed range; and the second photomask has a pattern isolating a real-pattern-formed region from a dummy-pattern-formed region. In forming the pattern, after forming a film to be processed on a substrate, a first mask is formed on the film to be processed,by lithography, using the first photomask, and a second mask is formed on the film to be processed, by lithography, using the second photomask. Thereafter, the film to be processed is etched and removed using the first and second masks as masks to form the pattern.