To provide a power plant facility having high responsiveness to fluctuations in the demand power of a system and capable of optimizing the fuel consumption of a diesel engine.

A power plant facility includes: a diesel main engine 1; a supercharger 2; an extracted gas bypass pipe 8 which is provided such that part of exhaust gas from the diesel main engine 1 bypasses the supercharger 2; an extracted gas bypass valve 9 which is provided in the extracted gas bypass pipe 8 and adjusts the amount of bypass of the exhaust gas; an exhaust gas economizer 3 which recovers exhaust heat from the exhaust gas to generate steam; a steam turbine 5 which is driven by the steam generated by the exhaust gas economizer 3; a power generator 7 which generates electric power by drive force obtained from the steam turbine 5 and supplies the generated electric power to an inboard system 34; and a control unit 10 which adjusts the degree of opening of the extracted gas bypass valve 9 according to the pressure of superheated steam to be supplied from the exhaust gas economizer 3 to the steam turbine 5.