To facilitate volumetric dilution when the values of specific gravity are different by a method in which after a strong acid solution being sent form a raw liquid tank to a strong acid measuring tank, given volume of the acid solution is sent to a weighing column, pure water of a pure water measuring tank is sent the column to dilute the acid.

In the precision dilution of a strong acid with strong corrosion power such as hydrofluoric acid, first hydrofluoric acid is injected into a raw liquid tank 10, and an air valve AV 11 is closed when a necessary quantity of hydrofluoric acid is stored. Next, the acid is pumped up into a strong acid measuring tank 20, and an air valve AV 13 is closed when the acid reaches regulated volume, the acid is dropped into a weighing column 40, and an air valve AV 14 is closed when regulated volume of the acid is stored. At the same time, an air valve AV 32 is opened, pure water is injected into a pure water measuring tank 30, an air valve AV 33 is opened, and pure water is dropped into the weighing column 40. After that, compressed nitrogen gas is supplied to the column 40, and the obtained diluted hydrofluoric acid is sent from the column 40 to output piping.