A plant-cultivating method is provided which comprises a step (A) of irradiating a plant with a red light and a step (B) of irradiating a plant with a blue light, wherein the step (A) and the step (B) are independently carried out for a predetermined period of time under cultivation conditions such that a fertilizer is used for each of the step (A) and the step (B), of which at least the fertilizer used for the step (A) is applied in the form of a nutritious liquid containing fertilizer ingredients and further carbon dioxide added therein. Preferably, a nutritious liquid is applied at each of the step (A) and the step (B), and the nutritious liquid applied at the step (A) contains carbon dioxide at a concentration higher than that in the nutritious liquid applied at the step (B).
