A marine vessel propulsion device attachable to a marine vessel (V1) and comprising: a duct ; a propeller that is rotatable with respect to the duct around a propeller axis (A2), the propeller including a plurality of blades and a rim that surrounds the plurality of blades , the propeller being surrounded by the duct ; and an electric motor that includes a stator and a rotor , and that rotates the propeller by rotating the rim with respect to the duct , a bracket that is attachable to the marine vessel (V1), wherein the duct is rotatable around a vertical or substantially vertical steering axis (A1) with respect to the bracket , the propeller axis (A2) extending in a direction perpendicular or substantially perpendicular to the steering axis (A1), and a motor electronic control unit is mounted in the marine vessel propulsion device , said motor electronic control unit is electrically connected to the electric motor and adapted to control said electric motor ; and an output adjusting device is adapted to perform an output adjustment of the marine vessel propulsion device , wherein the output adjusting device is electrically connected to the motor electronic control unit , wherein the electric motor includes the stator defined by at least one portion of the duct and the rotor defined by at least one portion of the rim , and based on an output command that has been input from an output adjusting device , the motor electronic control unit is configured to control a power supply to the stator , characterized in that the marine vessel propulsion device comprises a motor rotation angle detector detecting the rotation angle of the rotor with respect to the stator, so that based on an output generated by the motor rotation angle detector , the motor electronic control unit is configured to control the power supply to the stator 24, and hence configured to control a rotation direction and the rotation speed of the rotor . a duct ; a propeller that is rotatable with respect to the duct around a propeller axis (A2), the propeller including a plurality of blades and a rim that surrounds the plurality of blades , the propeller being surrounded by the duct ; and an electric motor that includes a stator and a rotor , and that rotates the propeller by rotating the rim with respect to the duct , a bracket that is attachable to the marine vessel (V1), wherein the duct is rotatable around a vertical or substantially vertical steering axis (A1) with respect to the bracket , the propeller axis (A2) extending in a direction perpendicular or substantially perpendicular to the steering axis (A1), and a motor electronic control unit is mounted in the marine vessel propulsion device , said motor electronic control unit is electrically connected to the electric motor and adapted to control said electric motor ; and an output adjusting device is adapted to perform an output adjustment of the marine vessel propulsion device , wherein the output adjusting device is electrically connected to the motor electronic control unit , wherein the electric motor includes the stator defined by at least one portion of the duct and the rotor defined by at least one portion of the rim , and based on an output command that has been input from an output adjusting device , the motor electronic control unit is configured to control a power supply to the stator , characterized in that the marine vessel propulsion device comprises a motor rotation angle detector detecting the rotation angle of the rotor with respect to the stator, so that based on an output generated by the motor rotation angle detector , the motor electronic control unit is configured to control the power supply to the stator 24, and hence configured to control a rotation direction and the rotation speed of the rotor . <EOS>