An outboard motor is equipped with a centrifugal clutch located between the crankshaft of an engine and a rotor of an electric motor for, when the engine operates, transmitting its output to through the rotor to a propeller, and with a motor output transmission mechanism for, when the engine does not operate, transmitting the output of the motor to the crankshaft. The engine can therefore be started by the motor used to drive the propeller. As a result, there is no need to install a separate electric motor for engine starting, so that starting of the engine by electric power can be made possible with minimum increase in the size and cost of the outboard motor.