There are disclosed a reductase having good heat stability, which resulted in decrease in reaction time and improvement of reaction efficiency. Specifically, disclosed is an enzyme having an amino acid sequence of SEQ ID NO:1 in which at least one of the amino acids of the positions 245 and 271 of the amino acid sequence of SEQ ID NO:1 is replaced with another amino acid(s); a polynucleotide having a nucleotide sequence that encodes the amino acid sequence of said reductase; a vector containing said polynucleotide; a transformant containing said polynucleotide or said vector, and the like.