To provide a marine propulsion system and an employment method of the same capable of observing new regulations applied to an engine exhaust gas regulation sea area without installing an exhaust gas denitrizer and an exhaust gas desulfurizer or changing fuel oil into low sulfur fuel oil.

The system comprises: a diesel engine 11 for rotating and driving a propeller shaft 21 and a screw propeller 22; and a steam turbine 12 rotated and driven by steam generated in a boiler 13 and rotating and driving a propeller shaft 36 and a screw propeller 31 which are different from the propeller shaft 21 and the screw propeller 22.