The Kosaka Mine Office was built in 1905 and used as the head office of Kosaka Smelting and Refining Co. Ltd. until 1990. In 1997, the Mine Office was scheduled to be destroyed to make way for a new smelter, but instead it was donated to the town. The Mine Office was disassembled and rebuilt next to the Korakukan, utilizing 90% of its original materials. It now serves as a museum of Kosaka’s mining history. The building is also partly used as an office for the town hall’s Tourism and Bureau division. The Mine Office was designated as a National Important Cultural Property of Japan in 2002.