Abstract: A control apparatus for controlling a delivery flow rate of a pump pressure-feeding process liquid within a process pipe system is described. The control apparatus has detecting means for detecting available N.P.S.H. of a pump on the basis of a pressure and a temperature of the process liquid within the suction portion of the pump, and calculating means for calculating an allowable maximum flow rate of the pump so as to hold the relationship: available N.P.S.H. required N.P.S.H. The control apparatus also has outputting means for outputting a control signal to control the delivery flow rate of the pump on the basis of the smaller value, the allowable maximum flow rate or a required flow rate of the pump.