Durability of formate dehydrogenase is improved with the use of formate dehydrogenase exhibiting high specific activity that is unpredictable from conventional findings. A specific amino acid substitution is introduced into Gibberella zeae-derived formate dehydrogenase. Mutant formate dehydrogenase exhibits durability that is extremely superior to that of wild-type formate dehydrogenase. Thus, the productivity of NADH that is produced using the mutant formate dehydrogenase can be improved.