1. An exposure method using a complementary divided mask comprising: a first step for detecting positions of alignment marks provided at the respective exposure objective unit regions, aligning the complementary divided mask based on said detected positions of alignment marks, and exposing the respective exposure objective unit regions in a first region including a plurality of exposure objective unit region at the middle portion of a semiconductor wafer; and a second step for determining coordinates of exposure objective regions in a second region, outside of said first region, where alignment of said complementary divided mask by detection of alignment marks cannot be used, aligning said complementary divided mask based on said positions of alignment marks detected in said first step, and exposing the regions in said second region.