Ph.D(Education). After working as a mathematics teacher at junior and senior high schools for 16 years, he worked as a senior researcher at National Institute for Educational Policy Research, and is currently a professor at the Graduate School of Education, Tokyo Gakugei University. Editor-in-Chief, Journal of Japan Society of Mathematical Education; Visiting committee member of Ministry of Education, Culture, Sports, Science and Technology; Visiting researcher, National Institute for Educational Policy Research.