Abstract
A cascade of two ring cyclotrons for the RIKEN RI beam factory are being constructed to provide primary heavy ions, up to uranium ions, with energies exceeding 100MeV/nucleon. The one in the second stage is a large-scale superconducting ring cyclotron with six sector magnets. The concept of the superconducting ring cyclotron design and status of the construction of its full-scale prototype are described. Compact superconducting cyclotrons now operating around the world are also introduced.