Flash smelting furnace at Saganoseki was build 1973 and its capacity increased to 3.5 times the original during 40 years. The degradation progressed in that process, so it was replaced to higher potential furnace in the long-term shutdown at 2017 for further capacity improvement. In addition, gas treatment facility for FSF off gas and other related facilities were modified in order to accommodate the increased FSF capacity. As a result, FSF capacity increased to 4 times the original after the long-term shutdown at 2019 and the competitiveness of Saganoseki smelter and refinery was improved.