PURPOSE: To improve the accuracy in a wide flow rate range from large to small flow rates by providing a capacity type flowmeter in a flow dividing pipeline, and providing a control valve in place of a venturi tube in a main pipeline.

CONSTITUTION: The flow rate of fluid flowing in a main pipeline 3 is controlled with a control valve 6, and the distributed flow rate of the fluid flowing in a flow dividing pipeline 4 is measured with a flowmeter 5. The valve 6 is held closed while the flow rate of the flowmeter 5 maintains a prescribed value; therefore, the signal from a pulse transmitter 7 is transmitted with a control circuit 8 to an arithmetic circuit 12. The flow rate calculated by said circuit is integrated and displayed as it is on a display meter 9. When a valve 2 is further opened and the flow rate of the flowmeter 5 attains the prescribed value or above, the calculation program stored in a storage circuit 11 is fed with a control device 8 to a valve driving part 10, which opens the valve 6 by as much as said value.