An object of the present invention is to identify a novel gene that effectively increases plant biomass and to provide said gene as well as techniques utilizing the same.This invention provides a nucleic acid encoding a protein, wherein the protein comprises the amino acid sequence of SEQ ID NO:1 and an amino acid sequence having at least 25% identity or at least 75% similarity to the amino acid sequence of SEQ ID NO:7 or 11, and has an activity to increase plant biomass, as well as techniques utilizing the same.
