Mt. Nantai in Nikko, Tochigi Pref. has been famous for being an object of faith since before Nara period. On the basis of this faith, the Nikko Shugendo-a religious body, whose activity was to take ascetic excercise only in mountains-was organised in Kamakura period. Shugendo is a religion peculiar to Japan, which is founded on Buddhism, Taoism and other thoughts. The Nikko Shugendo sought its origin to St. Shodo who was the first Buddhist climbed to the top of Mt. Nantai in Nara period, and it laid down the way of exercises or manners based on St. Shodo's biography "Hodarasan Konryuu Shugyo Nikki". Although it is recorded that this biography was written in early time of Heian period, it was written in Kamakura period in fact and a lot of incorrectness about St. Shodo's career or behavior was told. Therefore it is totally useless as a historical record. My study, does not show the proof of incorrectness, but mentions the reason why this biography was needed in Kamakura period. By studied actual way of exercis in mountains and St. Shodo's real life, I concluded that the biography had been written as a principle for organizing Nikko Shugendo as a religious body, and for that some untruths were required.