In Meiji 38 (1905), when the government’s monopolization of salt was enforced at the Higashihama Salt Farm, whose development had primarily been due to the work of the Asano family, the area of the farm was around 152 hectares. In Taisho 13 (1924), under the government monopoly, the Ako Higashihama Credit, Purchasing, and Use Cooperative Association was formed. The association assumed responsibility for things such as improving the efficiency of the salt production business, managing labor relations, and providing worker benefits. These documents contain records spanning roughly half a century until the association’s dissolution in Showa 47 (1972), covering the tumultuous time from the Taisho period to the Showa period and showing us the trends and technological innovations that occurred. These precious documents contain records showing the state of the salt business during the 20th century, and in Heisei 12 (2000), the collection was designated as a Cultural Property of Ako City.