Boat comprising: a power source (66,67); a remote control unit provided in a hull; and a boat propulsion unit controlled through the remote control unit so as to produce thrust, a steering wheel unit including a steering wheel ECU and a steering wheel, a key switch unit; a steering ECU connected to a steering motor of a steering actuator, the power source (66,67) being connected to the remote control unit and the boat propulsion unit via at least two systems of power supply lines (f), and the remote control unit and the boat propulsion unit being connected to each other via at least two systems of two DBW CAN cables as communication lines (e1, e2), the steering wheel unit and remote control unit being connected to each other via at least two systems of two DBW CAN cables as communication lines (e1, e2), the steering ECU and the boat propulsion unit being connected to each other via an at least two systems of two DBW CAN cables as communication lines (e1, e2), the remote control unit includes a remote control ECU, the rotational position of a remote control lever is detected by a position sensor, the position sensor is connected to the remote control ECU via at least two systems of analog signal lines (b), a power trim and tilt switch is connected to the remote control ECU via a signal circuit (b), the key switch unit is connected to the remote control ECU of the remote control unit, the key switch unit is provided with a start switch and a main/stop switch, the start switch and the main/stop switch are connected to the remote control ECU via signal circuits (b), the steering wheel is connected to a position sensor for detecting the position of the steering wheel, the position sensor is connected to the steering wheel ECU via signal circuits (b), a reaction force motor for applying reaction force to the steering wheel is connected to the steering wheel ECU via a drive system circuit (d), and a display/control section for changing the mode of a steering system is connected to the steering wheel ECU via a drive system circuit (b), the steering wheel ECU of the steering wheel unit is connected to the remote control ECU of the remote control unit via two DBW CAN cables as communication lines (e1, e2), the boat propulsion unit includes an engine ECU connected to a starting system, an ignition system and a fuel injection system via drive system circuits (d), the engine ECU is also connected to a throttle motor of a throttle body via a drive system circuit (d), the throttle opening of a throttle valve is controlled through the throttle motor, the throttle body is provided with a throttle position sensor for detecting the throttle opening, a signal from the throttle position sensor is input to the engine ECU. a power source (66,67); a remote control unit provided in a hull; and a boat propulsion unit controlled through the remote control unit so as to produce thrust, a steering wheel unit including a steering wheel ECU and a steering wheel, a key switch unit; a steering ECU connected to a steering motor of a steering actuator, the power source (66,67) being connected to the remote control unit and the boat propulsion unit via at least two systems of power supply lines (f), and the remote control unit and the boat propulsion unit being connected to each other via at least two systems of two DBW CAN cables as communication lines (e1, e2), the steering wheel unit and remote control unit being connected to each other via at least two systems of two DBW CAN cables as communication lines (e1, e2), the steering ECU and the boat propulsion unit being connected to each other via an at least two systems of two DBW CAN cables as communication lines (e1, e2), the remote control unit includes a remote control ECU, the rotational position of a remote control lever is detected by a position sensor, the position sensor is connected to the remote control ECU via at least two systems of analog signal lines (b), a power trim and tilt switch is connected to the remote control ECU via a signal circuit (b), the key switch unit is connected to the remote control ECU of the remote control unit, the key switch unit is provided with a start switch and a main/stop switch, the start switch and the main/stop switch are connected to the remote control ECU via signal circuits (b), the steering wheel is connected to a position sensor for detecting the position of the steering wheel, the position sensor is connected to the steering wheel ECU via signal circuits (b), a reaction force motor for applying reaction force to the steering wheel is connected to the steering wheel ECU via a drive system circuit (d), and a display/control section for changing the mode of a steering system is connected to the steering wheel ECU via a drive system circuit (b), the steering wheel ECU of the steering wheel unit is connected to the remote control ECU of the remote control unit via two DBW CAN cables as communication lines (e1, e2), the boat propulsion unit includes an engine ECU connected to a starting system, an ignition system and a fuel injection system via drive system circuits (d), the engine ECU is also connected to a throttle motor of a throttle body via a drive system circuit (d), the throttle opening of a throttle valve is controlled through the throttle motor, the throttle body is provided with a throttle position sensor for detecting the throttle opening, a signal from the throttle position sensor is input to the engine ECU.