The object is to search for a transcription factor having a novel function selectedfrom the function of increasing the plant body weight per plant individual, thefunction of increasing the weight of a specific plant tissue per plant individualand the function of increasing the productivity of a specific substance per plantindividual, and to improve any one of the functions in a plant body. The plant bodyweight per plant individual, the weight of a specific plant tissue per plant individual,the productivity of a specific substance per plant individual, or the contentof a specific substance per specific tissue in a plant body can be increased byexpressing a transcription factor which is so modified as to have a reduced transcription-promotingactivity.
