PURPOSE: To improve the accuracy in the rate of supply and obtain uniform intended materials continuously by calculating the changing speed of the level or wight of the liquid or the like in a metering vessel when the supply of the liquid or the like into said vessel in a continuous supply system is stopped, and correcting the rate of supply with said value.

CONSTITUTION: For example, the level L in a metering vessel 1 for liquid is measured with a level gage 2, and the signal of the level L and the flow rate set value F0 from a setter (a) are inputted continuously to a computer 3. The upper limit L1 and lower limit L2 of the level are beforehand set with the computer 3, and when L=L1 is attained, the supply to the vesse 1 is stopped and only the delivery of the liquid from the vessel is continued. When L=L2 is attained, the supply to the vessel is resumed. From the time (t) when L1 attains L2 and L1- L2=ΔL, the changing speed V of the level is determined, and from the speed V, a flow rate conversion value A is calculated, thence F0-A=Bn is calculated, and a correction value Cn is determined. With F0+Cn set as a flow rate D, it is inputted to a controller (b), whereby a control valve 5 is controlled. In this way, the accuracy in the rate of supply is improved.