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 air in a ship, the exhaust air discharged from an exhaust gas source is discharged into the seawater from a pipe passing through a hull, and the discharge device is equipped with a primary seawater intake opened at the front part of the hull, a seawater duct provided at a position close to the rear of the bottom of the ship while having a seawater intake opened at the front part and an exhaust outlet opened at the rear part, a seawater pipe opened to a seawater passage in the seawater duct through the inside of the hull from the primary seawater intake, an exhaust gas pipe to lead the exhaust gas to the downstream side of the seawater pipe opening part in the seawater passage, and a force-feeding means to force-feed the seawater in the seawater pipe toward the opening to the seawater passage.