The present invention provides a method for cultivation of a genetically-modified plant that can highly produce a desired protein. More specifically, the present invention provides a method for cultivation of a genetically-modified plant comprising: cultivating the genetically-modified plant in a medium, wherein the genetically-modified plant is transformed by introducing an expression vector comprising a promoter regulating expression of RNA and a seed storage protein isolated from a plant that highly expresses RNA and the seed storage protein under a high nitrogen condition; and a polynucleotide encoding an objective protein, and wherein the medium is adjusted so that nitrate nitrogen is 70 mg/L to 750 mg/L and/or ammonium nitrogen is 70 mg/L to 750 mg/L for a definite period in a period from 30 days before an expected flowering date to a date on or before flowering of the genetically-modified plant.