A novel protein deamidase having an activity of directly acting on a side chain amide group of an asparagine residue in a protein to form a side chain carboxyl group and release ammonia, a microorganism that produces the same, a gene encoding the same, a method for producing the same, and use of the same are provided. A bacterium classified into the class Actinobacteria is cultured to generate protein deamidase, and the enzyme is collected from culture.