A marine vessel propulsion system, comprising: a right propulsion device (301; 501) and a left propulsion device (302; 503) arranged to be mounted on a hull on right and left sides thereof, respectively, so as to enable respective steering angles to change; a right operation lever (102a; 600a) and a left operation lever (102b; 600c) arranged to be operated by a marine vessel maneuvering operator to control the right and left propulsion devices (301, 302; 501, 503) to change respective shift states selected from among a forward drive state, a neutral state, and a reverse drive state; a right lever position sensor (102c; 601a) and a left lever position sensor (102d; 601c) provided correspondingly to the right and left operation levers (102a, 102b; 600a, 600c) and arranged to detect positions of the right and left operation levers (102a, 102b; 600a, 600c); and a control unit programmed to control, based on detection results from the right and left lever position sensors (102c, 102d; 601a, 601c), the shift states of the right and left propulsion devices (301, 302; 501, 503), wherein the control unit is programmed to control the shift state of the right propulsion device (301; 501) dependent on the position of the right operation lever (102a; 600a), and to control the shift state of the left propulsion device (302; 503) dependent on the position of the left operation lever (102b; 600c), the control unit is programmed to control, based on detection results from the right and left lever position sensors (102c, 102d; 601a, 601c), the steering angles of the right and left propulsion devices (301, 302; 501, 503), and the control unit is programmed to control the steering angle of the right propulsion device (301; 501) dependent on the position of the right operation lever (102a; 600a), and to control the steering angle of the left propulsion device (302; 503) dependent on the position of the left operation lever (102b; 600c). a right propulsion device (301; 501) and a left propulsion device (302; 503) arranged to be mounted on a hull on right and left sides thereof, respectively, so as to enable respective steering angles to change; a right operation lever (102a; 600a) and a left operation lever (102b; 600c) arranged to be operated by a marine vessel maneuvering operator to control the right and left propulsion devices (301, 302; 501, 503) to change respective shift states selected from among a forward drive state, a neutral state, and a reverse drive state; a right lever position sensor (102c; 601a) and a left lever position sensor (102d; 601c) provided correspondingly to the right and left operation levers (102a, 102b; 600a, 600c) and arranged to detect positions of the right and left operation levers (102a, 102b; 600a, 600c); and a control unit programmed to control, based on detection results from the right and left lever position sensors (102c, 102d; 601a, 601c), the shift states of the right and left propulsion devices (301, 302; 501, 503), wherein the control unit is programmed to control the shift state of the right propulsion device (301; 501) dependent on the position of the right operation lever (102a; 600a), and to control the shift state of the left propulsion device (302; 503) dependent on the position of the left operation lever (102b; 600c), the control unit is programmed to control, based on detection results from the right and left lever position sensors (102c, 102d; 601a, 601c), the steering angles of the right and left propulsion devices (301, 302; 501, 503), and the control unit is programmed to control the steering angle of the right propulsion device (301; 501) dependent on the position of the right operation lever (102a; 600a), and to control the steering angle of the left propulsion device (302; 503) dependent on the position of the left operation lever (102b; 600c).