Using an idealized modeling experiment, in which the East/Japan Sea is simplified as a small rectangular basin connected to a larger basin through an inflow/outflow (through flow) system, the effect of the Tsushima Warm Current on the East/Japan Sea (EJS) circulation has been investigated. As well known, the current supplies heat to the EJS and when the inflow is considered, the model ocean becomes warmer. The water flowing from the smaller basin into the larger basin is cooler than the western boundary current, and colder water is found near the outlet in the cases with the through flow. The inflow also brings variability from the larger basin into the smaller basin, and the cases with the through flow show greater variability.