When taking the person on the pivot chair, turning, and stopping it suddenly, the jerky nystagmus of tens of seconds called after nystagmus is evoked. It is known that the duration of this after nystagmus decreases by the rotational training (repetition of the rotational stimulation). This phenomenon is called "habituation" of Vestibulo-Ocular Reflex (VOR) system, and it is thought that the cerebellum deeply takes part. The exercise ability of the person with short duration of the rotational nystagmus is high, and there is a research that this is a result of the improvement of a variety of equilibrium functions. Therefore, it is useful for establishment of the effective training methods of equilibrium function and the development of the training device to know the mechanism of the habituation in detail. This research tries to explain the habituation mechanism of the VOR system by using the learning theory of the cerebellum and verify the theory by the training experiment.