PROBLEM TO BE SOLVED: To provide a plant cultivation method and a plant cultivation device capable of increasing yield of plants having continuous light disorder without development of continuous light disorder even continuous light is applied to the plants.SOLUTION: There is provided a plant cultivation method in which plants having continuous light disorder are provided with circadian rhythm in which 1 cycle has 24 hours. The circadian rhythm is provided by continuously further irradiating light from an assistant light source consisting of a blue light source for 1 to 23 hours subsequent to no irradiation of light from the assistant light source while irradiation of continuous light from a main light source onto the plants for 24 hours.
