A new electrostatic ion storage ring, the RIKEN cryogenic electrostatic ring, has been commissioned with a 15-keV ion beam under cryogenic conditions. The ring was designed with a closed ion beam orbit of about 2.9 m, where the ion beam is guided entirely by electrostatic components. The vacuum chamber of the ring is cooled using a liquid-He-free cooling system to 4.2 K with a temperature difference of 0.4 K at most within all the positions measured by calibrated silicon diode sensors. The first cryogenic operation with a 15-keV Ne+ beam was successfully performed in August 2014. During the measurement, the Ne+ beam was stored under a ring temperature of 4.2 K with a residual-gas lifetime of more than 10 min. This permits an estimation of the residual gas density at a few 104 cm−3, which corresponds to a room-temperature-equivalent pressure of around 1×10−10 Pa. An effect of longitudinal pulse compression at the bunching cavity in the ring was clearly identified by monitoring the pick-up beam detector. Th...