A gene encoding a protein capable of controlling salt stress tolerance is provided. A polynucleotide encoding a plant gene capable of controlling salt stress tolerance is provided. The polynucleotide includes a polynucleotide which has a nucleotide sequence encoding an amino acid sequence from methionine at position 1 to asparagine at position 243 of SEQ ID NO: 2 in the sequence listing, or which has a nucleotide sequence encoding the amino acid sequence having one or several amino acid deletions, substitutions and/or additions and is capable of controlling salt stress tolerance.