The vacuum vessel of JT-60, JAERI large tokamak device whose construction has just been started in fiscal year 1977, is a toroidal chamber made from Inconel 625 and consists of eight rigid sectorial rings and U-shaped parallel bellows. It has a major radius of 3m, a non-circular cross section with a bore of 3m and an electric resistance of 1.3mΩ. The ultimate vacuum pressure is less than 10-8 torr. The vessel is loaded by atmospheric pressure and various electromagnetic forces during a discharge at a temperature up to 400°C. Construction of such a large vacuum vessel as in the JT-60 has never been made in the past and necessitated to undertake a series of research and development (R & D) regarding selection of vacuum vessel materials, manufacture of components, selection of surface treatment technique and methods for analyzing stress, strain, buckling and temperature distribution of the vacuum vessel. The present R & D was completed and established design and fabrication technique for the construction of the JT-60 vacuum vessel with such satisfactory results that Inconel 625 was selected as the vacuum vessel material, fabrication technique of bellows with a non-circular cross section was established, the availability of the surface treatment technique was verified and a new finite element method specially suited for the stress analysis of such structures was developed.