Abstract: In a nuclear fusion device having a torus type vacuum shell around which toroidal coils and poloidal coils are wound and arranged and whose interior is maintained in a high vacuum state, the bending rigidity of a shell wall in a circular cross section of the vacuum shell is made higher on the outer periphery side than on the inner periphery side of the circular cross section, thereby to prevent any deformation of the vacuum shell due to a magnetic force and any damage of the shell attendant upon the deformation in a process in which the coils are energized to confine a plasma within the vacuum shell. Moreover, without increasing the inner diameter of the circular cross section of the vacuum shell, the coils are located in proximity to the plasma so as to enhance the plasma producing efficiency.