For the ancient nation of Japan, the area corresponding to present-day Yamaguchi Prefecture was a major source of copper. Copper produced in this area played an important role in ancient society, being used as material for the Great Buddha statue and coins in Nara. However, the prehistory of the region, i.e., the situation before the related industries were brought under the direct control of the central government in the early 8th century, has not been fully examined. This paper, therefore, first outlines the conditions under which related industries have flourished in the region since the Yayoi period. It will also elucidate that the roots of the technology can be found on the Korean Peninsula. The paper also points out that the existence of such industries in the region was a precondition for the central government to take direct control of the region.