From 2000 to 2003 he was a Research Associate with School of Science and Engineering,
Waseda University, Tokyo, Japan; from 2004 to 2010, Research Associate then Assistant Professor with College of Science and Engineering, Aoyama
Gakuin University, Kanagawa, Japan; from 2012 to 2018, lecturer, Associate Professor and then Professor with School of Network and Information, Senshu
University, Kanagawa, Japan. Since 2019, he has been a Professor at Center for Data Science, Waseda University, Tokyo, Japan.