An intrinsic feature of a pre-modern society is its diversity of industries and its fragmentary markets. Fragmentary markets are more likely to fail in coordination of resource allocation. However, if a concentrated market is exogenously formed and the market could provide the only price to local markets, the market can work as a pivot of coordination for development. Treaty port markets imposed on nineteenth-century Japan worked as the pivot and ignited Japanfs industrialization. This work examines the silk-reeling industry, which was the major exporter and led Japanese industrialization, and role of treaty ports in its development.