A vessel propulsion apparatus comprising: a hub arranged on and receiving power through a main shaft; main blades installed on the outer circumferential surface of the hub; sub-blades spaced and placed toward the back of the main shaft from the main blades and installed inclined toward the back of the main shaft; and a duct installed around the main blades, and having an airfoil section, wherein the duct comprises a nose as a front vertex of an airfoil section, and a tail as a rear vertex of the airfoil section, characterized in that: the sectional shape of the duct comprises: an outer surface formed convex upward at the front end of the duct, and formed concave downward at the back end of the duct; and an inner surface, the inner surface comprising: an inner front portion of the duct formed convex downward at the front end of the duct; an inner rear portion of the duct formed convex downward at the back end of the duct; and a parallel portion running parallel with a rotation axis of a propeller of the apparatus and seamlessly connecting the inner front portion of the duct with the inner rear portion of the duct, and wherein the sub-blades are positioned in a range of 0.5 relative to the full length of the duct toward the back of the main shaft from the position of the main blades. a hub arranged on and receiving power through a main shaft; main blades installed on the outer circumferential surface of the hub; sub-blades spaced and placed toward the back of the main shaft from the main blades and installed inclined toward the back of the main shaft; and a duct installed around the main blades, and having an airfoil section, wherein the duct comprises a nose as a front vertex of an airfoil section, and a tail as a rear vertex of the airfoil section, characterized in that: the sectional shape of the duct comprises: an outer surface formed convex upward at the front end of the duct, and formed concave downward at the back end of the duct; and an inner surface, the inner surface comprising: an inner front portion of the duct formed convex downward at the front end of the duct; an inner rear portion of the duct formed convex downward at the back end of the duct; and a parallel portion running parallel with a rotation axis of a propeller of the apparatus and seamlessly connecting the inner front portion of the duct with the inner rear portion of the duct, and wherein the sub-blades are positioned in a range of 0.5 relative to the full length of the duct toward the back of the main shaft from the position of the main blades. an outer surface formed convex upward at the front end of the duct, and formed concave downward at the back end of the duct; and an inner surface, the inner surface comprising: an inner front portion of the duct formed convex downward at the front end of the duct; an inner rear portion of the duct formed convex downward at the back end of the duct; and a parallel portion running parallel with a rotation axis of a propeller of the apparatus and seamlessly connecting the inner front portion of the duct with the inner rear portion of the duct, and wherein the sub-blades are positioned in a range of 0.5 relative to the full length of the duct toward the back of the main shaft from the position of the main blades. an inner front portion of the duct formed convex downward at the front end of the duct; an inner rear portion of the duct formed convex downward at the back end of the duct; and a parallel portion running parallel with a rotation axis of a propeller of the apparatus and seamlessly connecting the inner front portion of the duct with the inner rear portion of the duct, and wherein the sub-blades are positioned in a range of 0.5 relative to the full length of the duct toward the back of the main shaft from the position of the main blades.