In an outboard motor conversion unit, it is configured to have a boat-side conversion unit that detects displacement generated at a movable member due to manual manipulation of a mechanical operation mechanism and converts the detected displacement into an electric signal, actuators connected to a steering mechanism, a shift mechanism and a throttle valve of an internal combustion engine of the outboard motor, and an actuator controller that controls operation of the actuators based on the converted electric signal. With this, the outboard motor installed at a boat with the mechanical operation mechanism can be easily converted to an electronically-operated outboard motor without newly installing a remote control unit or the like.