cultivating the plant without replenishing a fresh nutrient solution at an initial cultivation stage continuing the cultivation with the fresh nutrient solution replenished by an amount compensating for the spontaneous loss in the nutrient solution at a medium cultivation stage and then conducting the cultivation with supplying the fresh nutrient solution by an amount exceeding the spontaneous loss in the nutrient solution at a later cultivation stage. The amount of the nutrient solution replenished at the later cultivation stage is increased as the cultivation proceeds.