Myogaku (1056-year of death unknown) was a priest of the Tendai sect in the late Heian period. Myogaku's name was also read as Meikaku. He adopted the name of Onsenbo or Yuishinbo (unconfirmed).
Myogaku entered the temple on Mt. Hiei and learned about the Tendai sect under Kakugen. He revered Annen (841?-915?) who founded the Godai-in Temple in Mt. Hiei while studying Shittan gaku (the study of the phonetics of Sanskrit), then moved to Onsen-ji Temple in the Kaga Province to live. He wrote books on Shittan gaku and was respected as the founder of the study in later years. He also left behind many contributions for rendering Chinese into Japanese for Buddhist scriptures using guiding (punctuation) marks. Among many others, he wrote the "Shittan Yoketsu" (a book of Sanskrit study), "Bonjigyo Ongi," and "Hanon Saho" (a book of phonology).
In his books, Myogaku described the methods of Hansetsu (Chinese phonology "fanqie": a method to indicate the pronunciation of a kanji character by using two other characters) by using kana (the Japanese syllabary) from the 'Gojuonzu' ("fifty-sound" syllabary chart). Myogaku is considered to have compiled a treatise explaining the pronunciations and meanings of kanji for the "Hoke-kyo" (the Lotus Sutra), in which he categorized Japanese pronunciations of kanji with consonants and vowels at the end of syllables in Chinese and made such distinctions as those between the symbols for "u" and "ug" for sequential voicing. This treatise was later called 'Myokaku Sanzoryu' and distributed with added Japanese readings of Chinese characters. Most of the Hansetsu of the "Hoke-kyo Tanji" correspond to the Hansetsu of Myogaku's treatise and both are considered to be based on the same phonology system.