RIKEN has built nine cyclotrons so far. The third RIKEN cyclotron was moved from Komagome, the former RIKEN site, to Wako campus in March 2021. It is good chance to describe its historical significance and the details of its design, looking back at the history of the RIKEN cyclotrons. Finally, if we were to revive this No. 3 cyclotron, I would consider what use it might have.