To provide an underwater discharge device for exhaust gas in a ship, capable of raising propulsion efficiency of the ship and absorption efficiency of carbon dioxide with a simple and inexpensive means and without requiring any special device, by efficiently using energy of the exhaust gas and energy caused by navigation of the ship, when making the seawater absorb carbon dioxide in the exhaust gas while obtaining propulsion force of the ship by the seawater mixed with the exhaust gas.

In this underwater discharge device for exhaust gas in a ship, the exhaust gas discharged from an exhaust gas source discharged into the seawater from a pipe passing through a hull, and the discharge device is equipped with a seawater pipe made to pass through a hull and connected to an exhaust outlet provided on the bottom of the ship from a seawater intake opened at the front of the hull, a force-feeding means to force-feed the seawater in the seawater pipe toward the exhaust outlet, and an ejector device to suction the exhaust gas in an exhaust gas pipe branched from a discharge pipe by a venturi action caused by the flow speed of the seawater in the seawater pipe provided at the downstream location of the force-feeding means.