A twin-screw ship, comprising: a hull with a stern structure having a tip thereof oriented towards the stern located on a hull centerline; a port side propeller; a starboard side propeller; a rudder provided on the hull centerline backwardly from the port and starboard side propellers (20,10); a port side propeller axis provided to extend backwardly from the stern structure and connected at one end with said port side propeller and at the other end with a port side main engine in the hull; and a starboard side propeller axis provided to extend backwardly from the stern structure and connected at one end with said starboard side propeller and at the other end with a starboard side main engine in the hull, wherein said port and starboard side propellers (20,10), when the stern structure of the ship is viewed from the side of the bottom of the ship, are arranged on the sides of the hull centerline in symmetry with respect to the hull centerline and to be apart from each other by an inter-propeller-tip distance d which satisfies 0 ≤ d ≤ 0.5Dp, where Dp is the propeller diameter of said port and starboard side propellers (20,10), wherein the position of the tip of the stern structure which is provided at the same height as said port and starboard side propellers (20,10) is located on the bow side compared with the ends on the bow side of the rotation planes of said port and starboard side propellers (20,10), characterised in that said port and starboard side propellers (20,10) are configured to respectively rotate in outboard directions (P2,P1) in order to collect longitudinal vortices (V2,V1) of low-speed flows respectively rotating in inboard directions and generated in the neighborhood of the ship centerline to improve the propulsion performance, and in that said port side propeller axis is inserted into a port side propeller axis tube and said starboard side propeller axis is inserted into a starboard side propeller axis tube, and said starboard and port side propeller axis tubes (11,21) are external straight cylindrical pipes protruding from the stern structure towards the stern to protect the port and starboard side propeller axis (22,12), respectively. a hull with a stern structure having a tip thereof oriented towards the stern located on a hull centerline; a port side propeller; a starboard side propeller; a rudder provided on the hull centerline backwardly from the port and starboard side propellers (20,10); a port side propeller axis provided to extend backwardly from the stern structure and connected at one end with said port side propeller and at the other end with a port side main engine in the hull; and a starboard side propeller axis provided to extend backwardly from the stern structure and connected at one end with said starboard side propeller and at the other end with a starboard side main engine in the hull, wherein said port and starboard side propellers (20,10), when the stern structure of the ship is viewed from the side of the bottom of the ship, are arranged on the sides of the hull centerline in symmetry with respect to the hull centerline and to be apart from each other by an inter-propeller-tip distance d which satisfies 0 ≤ d ≤ 0.5Dp, where Dp is the propeller diameter of said port and starboard side propellers (20,10), wherein the position of the tip of the stern structure which is provided at the same height as said port and starboard side propellers (20,10) is located on the bow side compared with the ends on the bow side of the rotation planes of said port and starboard side propellers (20,10), characterised in that said port and starboard side propellers (20,10) are configured to respectively rotate in outboard directions (P2,P1) in order to collect longitudinal vortices (V2,V1) of low-speed flows respectively rotating in inboard directions and generated in the neighborhood of the ship centerline to improve the propulsion performance, and in that said port side propeller axis is inserted into a port side propeller axis tube and said starboard side propeller axis is inserted into a starboard side propeller axis tube, and said starboard and port side propeller axis tubes (11,21) are external straight cylindrical pipes protruding from the stern structure towards the stern to protect the port and starboard side propeller axis (22,12), respectively.