According to the present invention, a technique with which the production of plant biomass can be drastically increased and salt stress resistance can be imparted to a plant is provided. A gene encoding a protein comprising a common sequence consisting of the amino acid sequence shown in SEQ ID NO: 3 and a common sequence consisting of the amino acid sequence shown in SEQ ID NO: 2 in such order from the N-terminal side and having a coiled-coil structure, a nucleic acid binding site, and a leucine rich repeat structure has been introduced or an expression control region of the gene that is endogenously presented has been altered.