This invention provides a novel gene that can impart salt stress tolerance to plants for a long period of time and salt stress tolerant transgenic plants to which such gene has been introduced. Such novel gene encodes the following protein (a), (b), or (c), and such salt stress tolerant transgenic plant has such gene introduced therein: (a) a protein consisting of the amino acid sequence as shown in SEQ ID NO: 2 in the Sequence Listing; (b) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in SEQ ID NO: 2 in the Sequence Listing by deletion, substitution, or addition of one or several amino acid residues and having activity of imparting salt stress tolerance to plants; or (c) a protein consisting of an amino acid sequence derived from the amino acid sequence as shown in SEQ ID NO: 2 in the Sequence Listing by deletion, substitution, or addition of one or several amino acid residues and having UDP-glucose 4-epimerase activity.