A plant-cultivating method is provided which comprises a red light irradiation step (A) and a blue light irradiation step (B), wherein the step (A) and the step (B) are independently carried out for a predetermined period of time under cultivation conditions such that the temperature in a cultivation atmosphere at the step (A) is lower than that at the step (B). Preferably, the temperatures in a cultivation atmosphere at the step (A) and the step (B) are in the ranges of 12° C. to 19° C. and 20° C. to 25° C., respectively.