The number of people who are interested in Japanese mathematics classes has been increased since the mathematics education reform movements around the world in 1990s. The open-approach method is based on the tradition of Japanese mathematics education community in a sense that it made good characteristics of the tradition explicit and extended them. Therefore, its basic spirit, "be open both to students and to mathematics," can be a perspective for investigating Japanese lessons. In fact,this is consistent with the analysis of TIMSS Videotape Studies. When Stigler and Hiebert characterized the lessons in the US,Germany, and Japan in terms of relationships among students, teachers, and mathematics, they stated that students and mathematics were dominant in Japanese lessons (Stigler & Hiebert, 1999, pp. 25-26). Because of being open to both of students and mathematics, problem solving oriented lessons would result neither in teachers' demonstration of the best solutions nor in me representation of students' various opinions.