To improve ship energy efficiency by simple control.

A ship 1 comprises: a gas turbine 14 provided with a supercharger 22, and driven by exhaust gas of a main engine 12 for driving a propulsion propeller 29; a steam turbine 18 driven by steam generated by the exhaust gas; ship instruments 44 operating in response to supply of power generation electric power from a turbine generator 20; and an assisting engine 46 driven in response to the power generation electric power from the turbine generator 20, and assisting in the main engine 12. A ship propulsion device 10 drives the assisting motor 46 by a surplus electric power amount that is a difference between a power-generation electric power amount of the turbine generator 20 and a required electric power amount by the ship instruments 44, and reduces a bleeding amount of the exhaust gas bled to the gas turbine 14 when a consumed electric power amount of the assisting motor 46 reaches a preset electric power amount and the sum of the consumed electric power amount and the required electric power amount by the ship instruments 44 exceeds the power-generation electric power amount.