PURPOSE: To properly feed a solution to rock wool, etc., in water culture.

CONSTITUTION: Feed of a solution is started on signals from moisture sensors 6 and 7 and the solution is supplied through an integrating flowmeter 3 into rock wool heads 10 up to a prescribed amount determined by water level sensors 9. Excess water in the preset amount based on the aforementioned amount of the fed solution is then supplied. After feeding the solution up to the prescribed amount as described above, excess water is fed in the preset amount regardless of the above-mentioned amount of the fed solution.