The present invention provides a method for cultivating a plant seedling, which can cultivate a seedling causing no spindly growth, having a thick stem, and being favorably grown even after planting. The method for cultivating a plant seedling of the present invention is a method for cultivating a plant seedling by irradiation of a plant seedling with artificial light for promotion of growth, comprising continuously irradiating the plant seedling with blue illumination light for period (A), wherein 30% or more and less than 80% of the time taken for period (A) for continuously irradiating the plant seedling with blue illumination light corresponds to period (A-1) for continuously irradiating the plant seedling with blue illumination light and red illumination light.
