Abstract: Improving wild nitrile hydratase enables the provision of a protein which has nitrile hydratase activity and which has further improved heat resistance, amide compound resistance and high temperature accumulation properties. Use protein (A) or (B), (A) being a protein characterised by having nitrile hydratase activity and by including an amino acid sequence in which a specific amino acid residue in an amino acid sequence in wild nitrile hydratase has been substituted by another amino acid residue, and (B) being a protein characterised by having nitrile hydratase activity and by including an amino acid sequence in which one or several amino acid residues in the amino acid sequence of protein (A), other than the abovementioned specific amino acid residue, is deleted, substituted and/or added.