From 0.1° OFES (OGCM for the Earth Simulator) results provided by the JAMSTEC (Masumoto et al., 2004), we investigated the East China Sea circulation while focusing on the origin of the Tsushima Warm Current. The simulated sea surface temperature is cooler than the observation. The volume transport of the simulated Tsushima Warm Current is 1.7 Sv and is weaker than the observation. The Kuroshio Current, however, is reproduced well, as well as the Taiwan Warm Current of about 1.5 Sv. Considering that this global model is not optimized for the East China Sea, and these flows are not determined by the lateral boundary conditions but by the internal dynamics, the model results are good enough for the purpose of this study. The model results are analyzed while focusing on the interaction between the Taiwan Warm Current and the Kuroshio to determine the major source of the Tsushima Warm Current, and compared with earlier studies.