  Recently, a new concept, primitive chaos, was proposed, as a concept closely
related to the fundamental problems of physics itself such as determinism,
causality, free will, predictability, and irreversibility [J. Phys. Soc. Jpn.
{\bf 79}, 15002 (2010)]. This letter reveals a structure hidden behind the
primitive chaos; under some conditions, a new primitive chaos is constructed
from the original primitive chaos, this procedure can be repeated, and the
hierarchic structure of the primitive chaos is obtained. This implies such a
picture that new events and causality is constructed from the old ones, with
the aid of the concept of a coarse graining. As an application of this
structure, interesting facts are revealed for the essential condition of the
primitive chaos and for the chaotic behaviors.
