PURPOSE: To eliminate the evaporation of liquid chemicals by the influence of the b.p. and temp. thereof by providing a liquid chemical feed pipe of which the part near the top end is placed along a base of a vessel, providing many small holes atop the pipe of the part along the base and providing a liquid chemical press-feed means to a liquid chemical weighing vessel.

CONSTITUTION: The liquid chemical A is directly diffused through the small holes 6 provided to the feed pipe 2 into the liquid chemical B of the vessel 3 when pressure is exerted by a pump 4 to the feed pipe 2 to press-feed the liquid chemical A in the weighing vessel 1. Both liquid chemicals are thereby mixed. The evaporation arising from the b.p. and temp. of the liquid chemicals in the process for mixing the liquid chemical A and the liquid chemical B is thereby eliminated and there is simply the extremely slight evaporation from the surface of the liquid chemical B. The liquid chemical mixture having a specified mixing ratio is thus obtd. The quantitative control of the mixing ratio in the same manner is also possible even by using a metering pump in place of the quantitative control of the mixing ratio by the weighing vessel 1.