Provided is 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 is provided with: 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).