Provided is a method for improving the yield of a harvested product of at least one plant selected from the group consisting of plants belonging to the families Solanaceae, Cucurbitaceae, Poaceae and Fabaceae. A method for cultivating at least one plant selected from the group consisting of plants belonging to the families Solanaceae, Cucurbitaceae, Poaceae and Fabaceae comprises applying a plant-vitalizing agent comprising an exogenous elicitor and an endogenous elicitor to a young seedling of the plant at least one time.