This article intends to consider the origin of the notes, "半音"(Han-on; it means half sound) in the scores of Shōmyō. Also, it clarifies via what course it led for " 半音" to be used for the scores of Shōmyō. "半音 ", which was devised as the note to the closed syllable in Sanskrit language in the Ancient Chinese time was inherited to the research of Sanskrit in Japan and it was diverted to the scores of Shōmyō after that. It is estimated in the late Heian era.