PURPOSE: To enable the abnormal output of a flowmeter to be prevented or restrained even when a radioactive waste flowing in a pipeline contains bubbles by measuring and controlling a liquid in which solid matters, the bubbles and the like exist in said waste.

CONSTITUTION: The flow rate of a fluid mixed with sold matters, bubbles and the like and flowing in a pipeline 7 is measured by an electromagnetic flowmeter 1 and a Doppler flowmeter 2 and signals indicative of the flow rate is fed to a comparator 3, where the two signals are compared with each other. Then, after logically decided by a logical decision circuit 4, the signals are fed to a fixed displacement pump drive circuit 5, which drives a fixed displacement pump 6 to control the flow rate. On the other hand, sometimes the flow rate of the fluid mixed with the solid matters, bubbles and the like and flowing in the pipeline 7 causes the electromagnetic flowmeter 1 to produce an abnormal output, which is very difficult to be removed. However, the flow rate signals of the electromagnetic flowmeter 1 and the Doppler flowmeter 2 different from the electromagnetic flowmeter 1 in a measurement principle are compared with each other and, when the difference therebetween is judged to be large by the logical decision circuit 4, a control can be conducted by a preceding control signal and, when small, by the present control signal.