A plant-cultivating method is provided wherein a red light irradiation step (A) and a blue light irradiation step (B) are independently carried out for a predetermined time period, and far-red light is additionally irradiated concurrently with red light at step (A) or with blue light at step (B), or, with red light and blue light at step (A) and step (B), respectively. When far-red light is irradiated concurrently with red light at step (A), the emission intensity of red light is larger than that of far-red light, and an emission intensity ratio of red light to the total lights at step (A) is at least 50%. When far-red light is irradiated concurrently with blue light at step (B), the emission intensity of blue light is larger than that of far-red light, and an emission intensity ratio of blue light to the total lights at step (B) is at least 50%.
