In the deep sea area of the Japan Trench, located about 150 km east from northern Honshu, one observes southward flow on the landward slope and the northward flow on the oceanward slope. In 1994 and 1995, moorings were deployed on the Japan Trench landward slope around 40 ¿N. One mooring was deployed for 275 days at about 5800 m, and another mooring was deployed for 20 days at 4200 m depth. Results showed the following: (1) A deep western boundary current flows south-southwest on the landward slope of the Japan Trench with mean speed of 3--7 cm/sec and maximum speed of 15--20 cm/s. (2) Current changes depend mainly on the M2 tide. (3) Previous measurements, as well as inferences from observed benthic fauna, imply oppositely directed flow along the oceanward slope of the Trench, forming a trench countercurrent. ¿ 1998 American Geophysical Union