This paper discusses Inazou Nitobe's effort to interpret Japanese ideas toward westerners, especially focusing on the concept of "Kou" (filial duty). Nitobe (1872~1933) revised his well-known writing Bushido in 1905. At the preface in this revised edition, he mentioned the concept of "Kou," one of the traditional Japanese moral codes by devoting almost half of the space of the whole preface. However, what he stated here was simply that he was not able to write about it. It is pointed out that Nitobe's approach to writing Bushido is to make the "congruity" between Japanese ideas and western ideas. To put it an other way, Nitobe's comment at the preface will be a statement that 'Kou' is one of the most unique Japanese traditional moral concep...