A target protein is expressed in a bacterium having a type III secretion apparatus, and the bacterium is brought into contact with a plant, and then the infected tissue is cultured under a bacteriostatic condition for a certain period, thereby cultivating the bacterium-infected plant as it is. As compared with the conventional method, the present inventors have found that the efficiency of protein introduction into plants is dramatically increased.III型分泌装置を有する細菌で目的のタンパク質を発現させ、当該細菌を植物に接触させた後、感染組織を静菌的条件下で一定期間培養することにより、細菌感染させた植物をそのまま栽培する従来法と比較して、植物へのタンパク質の導入効率が飛躍的に高まることを見出した。
