Abstract
Until recently, the most westerly habitat of Clethrionomys rex was thought to be Kuromatsunaicho-utasai in the Shiribeshi-shicho Kannai area of Hokkaido. However, eleven Clethrionomys rex have been recently captured 18kms southwest of the upper reaches of the Kunnui River in Oshamanbe-cho, 120 meters above sea level. Thereby the authors have confirmed that the habitat of Clethrionomys rex extends further west than previously thought.
