Abstract: An object of the present invention is to provide a method of producing plant seeds for cultivation of the next generation which can be grown to plants with excellent yielding properties and cultivation properties while using an existing variety as such. In a cultivation space where the concentration of CO2 is controlled, for example, a semi-closed space such as a greenhouse or similar structures where the concentration of CO2 is controlled to be 200 ppm higher than that of the standard atmosphere, or a farm field utilizing a free-air carbon dioxide enrichment facility, plants which belong to grain crops, industrial crops, cattle feed crops/pasture grasses, vegetables and flowers are grown and seeds (plant seeds for cultivation of the next generation) are collected from the plants.