A ship propulsion device having an asymmetric duct is disclosed. A duct, which is a horizontally asymmetric structure, is formed in a shape that an upper chord becomes narrow and is applied to the ship propulsion device. A port support part having a fixed pitch angle is formed in the duct. Therefore, the present invention improves the propulsion performance of a ship while preventing the reduction of thrust generated in the upper area of the duct by preventing resistance from being generated due to flow separation caused by an excessive angle of attack in the lower area of the duct.
