Mitsubishi Heavy Industries, Ltd. (MHI) Group has been developing additive manufacturing (AM) as a method that can manufacture parts with complicated shapes and is considering its application to manufacturing processes. For large frame gas turbines, with the aim of improving performance by reducing the amount of cooling air for hot parts, the adoption of a complicated internal cooling structure, which cannot be made with conventional manufacturing methods but can only be made by AM, is being considered. AM is not a method that can build a practical part immediately when 3D CAD data is input to the building equipment, but a method that requires an innovative design concept based on the characteristics and restrictions of building objects, in addition to technological development for the optimization of building and post-processing conditions, quality assurance by in-process monitoring, etc. This report describes the development of metal AM technology for gas turbine components.