We are constructing an isochronous storage ring named “Rare-RI Ring (R3)” at RIKEN RI Beam Factory. R3 is the most favorable equipment for measuring the mass of rare-RIs in a precision of the order of ppm by using the relative TOF measurement method. Recently, we carried out a commissioning run using 78Kr beam and the basic performances of R3 were verified. In this article, we describe the history of the past, the results of the commissioning run, and future prospects.
