Several ground-based facilities have been developed for the study of hyper-gravity on Earth. Gravitational accelerator uses centrifugal force to make hyper-gravity condition. This machinery could be used not only for humans (for training of pilots), but also for experimental animals (basic research about its effect in vivo). In order to study the effect of long-term as well as short-term hyper-gravity on experimental animals, we developed Gravitational accelerator using rotatory centrifugal force. With 1 meter-long arms on both sides and with the rotational speed of 120 rpm, we could reproduce 15 Gz of hyper-gravity. We assured its stability and safety by operating it during 7 continuous days. After we made it certain that our Gravitational accelerator was well operated during that period, we performed additional study about the effect of hyper-gravity on the immune status of experimental animals.