Sea of Japan or East Sea, arm of the Pacific Ocean, lying between Japan on the east and the Asian mainland on the west. It is connected to the Sea of Okhotsk, on the north, by the La Pérouse Strait and the Tatar Strait; to the Pacific Ocean, on the east and south-east, by the Tsugaru Strait and the Bungo Strait, respectively; and to the East China Sea, on the south, by Korea Strait and Tsushima Strait. The sea is known as the East Sea in both North and South Korea. Area, about 1,013,000 sq km (391,100 sq mi).