In "Sengaikyo" (oldest topography of China), it was written that there is Kokushi-koku (literally, "black-teeth country"); in Gishi-wajin-den (the first written record of Japan's commerce) of the history book "Sangokushi" (Three Kingdoms of Saga), it was written as Wakoku Toho (eastern country, Japan).
山海経に黒歯国（『三国志(歴史書)』魏志倭人伝では倭国東方）があると記述がある。