The voltage-derived transport in the Korea Strait from March 1998 to April 2002 reveals various temporal variations such as subinertial, monthly, seasonal, and interannual variations. The driving mechanisms of these temporal variations in the flows through the straits and the mean sea level of the East Sea (Sea of Japan) are investigated using a simple analytical barotropic model. The East Sea is simplified as a flat-bottomed semienclosed basin, and it is forced by the atmospheric pressure, the along-strait wind stress, and the sea level differences along the straits. Despite its simplicity this model explains most variations and helps us understand dominant driving forces on each timescale. At the subinertial periods of 2--10 days the atmospheric pressure dominantly drives the flows into or out of the East Sea due to a Helmholtz resonance, whose period is about 3 days, and the mean sea level cannot respond isostatically. The effects of the atmospheric pressure on the transport variations become weak at long periods because there is enough time for the East Sea to be drained or filled through the strait flows as its mean sea level responds isostatically. On the other hand, the changes in the adjusted sea levels outside the straits of the East Sea cause the pressure gradient forces along the straits and induce most of variations in the strait flows and the mean sea level at the monthly to interannual periods.