To know flow rate in real time by providing a load sensor arranged between a pressure vessel and a pad, a solution sample vessel placed on the pad inserted with a liquid feeding tube, and a computing unit for controlling a valve controller based on a signal from the load sensor.

By controlling a valve 9 by an instruction of a computing unit 11 via a valve controller 13, and increasing a pressure in a pressure vessel 1 to a certain pressure and keeping it, the liquid level of a solution sample 5 contained in a vessel 6 is pressed and the solution sample 5 discharged to outside the pressure vessel 1 through a liquid feed tube 7 at a certain flow rate. At this time, a weight change of the solution sample 5 in the vessel 6 placed on a pad 4 is detected by a load sensor 2 placed between a support base 3 and the pad 4. This change quantity is fed to the computing unit 11 in read time. The calculation results are displayed on a display 12, and are reflected on switching control of the valve 9 via the valve control 13.