Hydrostatic Drive Systems have a demand-responsive pump and hydraulic circuit. It has a demand-responsive pump and at least one hydraulic circuit. The pressure-maintaining valve can be controlled by a differential signal formed from a load pressure signal and a delivery pressure signal. The load pressure signal to the pressure-maintaining valve can be changed by the output signal of a pressure-reducing valve. The pressure-maintaining valve can be pressurized with the output-side pressure of the pressure-reducing valve that is located in a load pressure line. The output pressure of the pressure-reducing valve can be adjusted by a spring and a variable control pressure.