Laser light in a pattern reflected by a two-dimensional array micromirror 106 that is controlled on the basis of mask data of a mask pattern data output device 107 forms an enlarged pattern 110. This enlarged pattern is projected in a reduced manner onto a mask substrate 109 through a reduction-projection optical system 102, thereby forming a lithography pattern 111. Since a large number of patterns are written in an instant by the two-dimensional array micromirror 106, a time required for lithography the entire mask pattern is extremely shortened as compared with a conventional one. As a result, the mask cost can be largely reduced.