The adverb “不得已” in Japanese means “unwillingly”, and its formation is different from original Japanese words. Furthermore, it is influenced by “不レ得レ已[已む（こと）を得ず”, which is the Kanbunkundoku of “不得已” in ancient Chinese. Based on the original Japanese word of “得る、已む”, “不得已” ancient Chinese was transformed into ancient Japanese by means of Kanbunkundoku. The Kanbunkundoku of “不得已” gradually pervaded into each era of the formation and development of Japanese. As a result, the word has been added to the Japanese dictionary as an independent adverb.