Steam conditions for large-capacity fossil-fuel-burning thermal power plant in Japan have conventionally been 24.1 Mpa 538/566°C. Mitsubishi Heavy Industries, Ltd. (MHI) has, through wide-scale development programs, set techniques for steam turbine design and materials at a high steam temperature and steam conditions of 24.1 Mpa and 593/593°C applied to large-capacity 1 000 MW turbines, the Matsuura No. 2 Unit for the Electric Power Development Co., Ltd. Based on our high-temperature design development, MHI has developed and manufactured the 1 000 MW turbine, Misumi No. 1 Unit, for Chugoku Electric Power Co., Inc., for the first time in the world with steam condition of 24.5 Mpa and 600°C and a steam reheating temperature of 600°C. The first steam admission of this unit was completed in December 1997, and underwent test runs and other tests before starting commercial operation in June 1998. This paper describes the design and operating features of Misumi No.1 Unit.