PROBLEM TO BE SOLVED: To provide a transformed plant having high xylem (secondary cell wall) productivity to be a row material of biofuel.SOLUTION: Provided is a transformed plant or its progeny transformed with a construct that expresses OsNST2 gene derived from rice or its homolog under a promoter that induces expression specifically in xylem-forming cells (NST3 or its ortholog promoter). Also provided is a method for increasing xylem production by transformation with the construct.