A steam power plant is suggested having, parallel to the high-pressure preheater passage (VW4 to VW6), a heat reservoir (A) which is loaded with preheated condensate in weak-load times. This preheated condensate is taken from the heat reservoir (A) for generating peak-load and inserted downstream of the high-pressure preheater passage (VW4 to VW6) into the condensate line (19.2) resp. the feed water container (8). Thus it is possible to quickly control the power generation of the power plant in a wide range without significantly having to change the heating output of the boiler of the steam generator (1). A steam power plant equipped according to the invention can thus be operated with bigger load modifications and also provide more control energy.