Annaka zinc refinery of Toho Zinc Co., Ltd. produces 100,000 tons of electrolytic zinc per annum with its zinc content over 99.995%, using zinc concentrate as the main raw material. The zinc smelting process in Annaka refinery is the hydrometallurgical method which consists of roasting, leaching, purification and electrowinning. The environment of zinc smelting business in Japan have been severer due to some operational cost increases. The high electric power price which keeps rising after the Great East Japan Earthquake disaster in 2011 have still been the biggest challenge. Under such circumstances, we renewed the obsolete No.1 electrolysis plant which had operated during more than 70 years. This report describes the improvement cost effect including the electricity power cost in Annaka refinery and some improvements of the new plant in the Start-up stage.