PURPOSE: To enable accurate flow measurement over a wide variety of flow area, by correcting and adding the amount of one pulse transmitted from the pulse transmitter of a flow meter to the amount corresponding to the flow every one pulse.

CONSTITUTION: The number of clock pulses of pulse interval of the pulses fed from the pulse transmitter 1 of the flow meter is counted at the counter circuit 3. Further, the memory circuit 4 storing the flow corresponding to the clock pulse number delivers the flow corresponding to the number of clock pulses fed from the counter circuit 3 and this flow is added at the addition circuit 5 and displayed at the display meter 6. Thus, accurate flow measurement can be made over a wide variety only in the specific flow area.