A steam turbine plant is provided with: a plurality of steam turbines; a multistage pressure condenser composed of a plurality of condensers which are respectively provided below the respective steam turbines so as to correspond to the plurality of steam turbines, and in which steam which is discharged from the respective steam turbines is condensed and accommodated as condensate; and a steam extraction section which introduces some of the steam in the steam turbine into condensate of the condenser corresponding to the lowest-pressure steam turbine among the plurality of condensers.