A boat propulsion system comprising: a hull; a plurality of boat propulsion units (3a to 3d) disposed on the hull, wherein each boat propulsion unit can switch between forward and reverse propulsion independently from the others and can be steered independently from the others, the plurality of boat propulsion units (3a to 3d) including a first port-side propulsion unit disposed to the left of a center line extending in the longitudinal direction of the hull, a second port-side propulsion unit disposed to the left of the first port-side propulsion unit, a first starboard-side propulsion unit disposed to the right of the center line, and a second starboard-side propulsion unit disposed to the right of the first starboard-side propulsion unit; an operation portion capable of commanding an operation at least in the longitudinal directions of forward and reverse, and the lateral directions of left and right; and characterized in that it further comprises a control unit configured to individually control the forward and reverse propulsion directions, the propulsion force, and the steer angle of the plurality of boat propulsion units (3a to 3d) such that when the control unit receives an operational command for operation in a lateral direction from the operation portion, a point of action of a first resultant force, which is the resultant force of propulsion force generated by the first port-side propulsion unit and the first starboard-side propulsion unit, is positioned behind a point of action of a second resultant force, which is the resultant force of propulsion force generated by the second port-side propulsion unit and the second starboard-side propulsion unit. a hull; a plurality of boat propulsion units (3a to 3d) disposed on the hull, wherein each boat propulsion unit can switch between forward and reverse propulsion independently from the others and can be steered independently from the others, the plurality of boat propulsion units (3a to 3d) including a first port-side propulsion unit disposed to the left of a center line extending in the longitudinal direction of the hull, a second port-side propulsion unit disposed to the left of the first port-side propulsion unit, a first starboard-side propulsion unit disposed to the right of the center line, and a second starboard-side propulsion unit disposed to the right of the first starboard-side propulsion unit; an operation portion capable of commanding an operation at least in the longitudinal directions of forward and reverse, and the lateral directions of left and right; and characterized in that it further comprises a control unit configured to individually control the forward and reverse propulsion directions, the propulsion force, and the steer angle of the plurality of boat propulsion units (3a to 3d) such that when the control unit receives an operational command for operation in a lateral direction from the operation portion, a point of action of a first resultant force, which is the resultant force of propulsion force generated by the first port-side propulsion unit and the first starboard-side propulsion unit, is positioned behind a point of action of a second resultant force, which is the resultant force of propulsion force generated by the second port-side propulsion unit and the second starboard-side propulsion unit.