Among numerous editions of commentaries on Sango-shiki (三教指帰), which was one of the renowned works of Rev. Kukai (空海) in his youth, it has been unanimously accepted that the oldest existing MS should be Sangyd-kanchushd (三教勘注抄), stocked in the Library of Koyasan-Hojuin (高野山宝寿院). This MS is supposed to have been made sometime during the period between late Heian and early Kamakura. Our recent investigation, however, has come to a different conclusion. A copy stocked in the Library of Reiyukai (霊友会) is considered to be older than Sangyokanchusho. In spite of some technical limitations, being a mere fragmentary excerpt from certain older commentary, Reiyukai Book not only well irrustrates the feature of the original text, but also keeps the Kana way of reading or pronunciation, which is vitally necessary for further advanced criticism. Besides, we are fortunately in a position to use the Introductory Chapter by the name of "Shikigo" (識語) written by Shoken (勝賢) of Daigoji Temple (醍醐寺). In the light of comparison with his Diary now stocked in the Tokyo National Museum Reiyukai Book including "Shikigo" can be considered Shoken's own hand writing. "Shikigo" tells us that the author of this commentary, which later became the source of the except, was "Atsumitsu". Basing on this description we have verified, through text-criticism, that he is "Fujiwara Atsumitsu (藤原敦光)". In addition to the Koyasan Edition, Sonkeikaku Library (尊経閣文庫) stores another copy of Ninnaji Temple (仁和寺). Comparison of these three issues, in our view, clarifies some aspects of the process of evolution of the Atsumitsu's Commetary. Reiyukai Book consisting of three volumes lacks Vol. III. However, its Appendix includes the parts which were eliminated in the Vol. I and II. It also supplies copies of Buddhist scriptures and of ancient dictionary, as well as of the chronological data of the Imperial House. Needless to say, these parts are indispensable as source material. Therefore, we, the co-authors, decided to publish the complete text of this Book in its original form (with the least possible emendations) for the convenience of the researchers interested in this field of study.