the narrative of "Oguri-hogan" -an epic- was composed by the race of outcast artistes in Japanese Middle Ages. It is a magnificient story about death and revival of a hero, The hero "Oguri" was the knight who rode the restivest horse named Onikage. Onikage appears and disapeans in afantastic and symbolic state. If we analyze the character of this world of Ogurihogan with a focus on the image of Onikage, we understand a hidden process of an establishmeut of this story based on the mixture and degeneration of Japanese ancient faith and legend. Onikage succeeds to the pedigree of worship of the horse called "Ryo" in ancient China. "Ryo" (a dragon) was a fantastic animal originated from a horse. But in ancient Japan they thought it a selected, reassuringly and fast running, specified horse, and a demon's messenger Ryome. of course nobody but demon could ride the horse. But in Middle Ages "Ryo" moreover implied "Saenokami", one of ancient unvisible demon that existed on a boundary-line detween the land of the living and Hades. Two images of Ryo were mingled. It's the image that was made through a joint festival of peasants and wandering out cast artistes who entered into peasants' festival. It's "Bato-kannon" -the Horse-headed Merciful Goddess. The substance of the image of Onikage is constituted of two demonism factors, "Ryo" and "Bato-kannon". When this epic was produced with a contact to worship of the horse, Oguni took a special capacity that enables to come and go between the land of the living and Hades in spite of his agony as human, and could be proved the heroic character as human. Onikage is the other self of Oguri, and also Oguri is the inseperable other self of Onikage. The Above-mentioned description is the argument of the first part of "the Ryo and the Bato-kannon".