To provide an underwater discharge device for exhaust gas from a ship absorbing carbon dioxide gas in the exhaust gas in the seawater, requiring no special device by effectively using energy of the exhaust gas and energy caused by sailing of the ship for obtaining propulsion of the ship by the exhaust gas mixed seawater and capable of increasing propelling efficiency of the ship and absorbing efficiency of the carbon dioxide gas by a simple and inexpensive means.

This underwater discharge device for the exhaust gas from the ship for discharging the exhaust gas in the seawater through an exhaust gas pipe, is featured by forming the catamaran ship type hull for forming hull parts on both sides of a ship's bottom recessed part by forming the ship's bottom recessed part by upwardly recessing a central part from the ship's bottom, having a force feed means arranged in a seawater pipe opening in the ship's bottom recessed part by penetrating through the inside of the hull from a seawater intake port opened in the bow and forcibly feeding the seawater in the pipe toward a hull rear part opening, and arranging an ejector device for sucking the exhaust gas in the exhaust gas pipe by the venturi action by a flow of the seawater in the seawater pipe in a downstream exhaust gas pipe confluent part of the force feed means.