PURPOSE: To feed the optimal diluted nutrient solutions to a plurality of different cultivation media by controlling with a micro computer a system wherein a diluted nutrient solution is prepared with a plurality of independent feeding or stopping means for raw solutions and raw water in a mixing tank and the prepared nutrient solution is fed in the cultivation media.

CONSTITUTION: In the control of a cultivation system with a micro computer wherein a diluted nutrient solution is prepared with a plurality of independent feeding or stopping means (e.g. A-1, A-2 and E) for raw solutions and raw water in diluted nutrient solution-feeding or stopping means (mixing tank C) and the prepared diluted nutrient solutions are fed in cultivation media with feeding or stopping means, the control is carried out as follows. A diluted nutrient solution comprising arbitrary components in an arbitrary mixing ratio and amounts required for the above-mentioned media set on the basis of solar radiation amounts, temperatures, humidities, medium water contents, the past data, etc., is fed into the media on a water level or position (e.g. a position in a pocket P) disposed in the mixing tank C so that the level of the remaining diluted nutrient solution in the mixing tank C is always maintained at the above-mentioned water level or position (DF is a water level-detecting means in the mixing tank C).