PURPOSE: To shorten the time when measurement is infeasible and to make the semi-continuous measurement of the rate of supply and the velocity of flow possible by using a flowmeter having a buret provided with a detecting means for the change in liquid column and a tank provided with a detecting means for the prescribed value of the liquid column.

CONSTITUTION: A flowmeter F having a buret B communicating with a detector PS in the lower part is provided, and a tank T is disposed on the side of the outflow passage P2 of said flowmeter F. The tank T is communicated with an outflow passage P2 in the down stream position of a valve V2 by a branch line P3, and a stop valve V3 is interposed in the mid-way of the line P3. A liquid level detector LS which detects the liquid level in the prescribed upper limit position of the tank T is provided to said tank and the installation height thereof is made lower by a suitable distance from the upper limit position of the liquid level of the buret B. During the injection of the liquid into the buret B, the liquid is supplied from the tank T. After the end of the injection to the buret, the liquid is replenished and injected into the tank while the liquid is supplied from the buret and upon ending of the replenishment, the liquid is supplied only from the buret.