A new species of stygobiontic interstitial annelid, Diurodrilus kunii sp. nov., is described based on material collected from medium sand sediment (φ = 1.2–1.7) at groundwater level (40–100 cm in depth; 5–15 m inland from splash zone) in the intertidal beach slope on Ishikari Beach, facing the Sea of Japan, Hokkaido, Japan. The new species differs from six known congeners in the arrangement of the anterior-head ventral ciliophores, the degree of development in the primary and secondary toes, and the shape of the spermatozoa. We inferred the phylogenetic position of the new species among other congeners for which 18S rRNA, 28S rRNA, and COI gene sequences were available in public databases. This is the first representative of the genus from the Northwest Pacific.