The present invention provides a DNA coding for a protein defined in the following (A) or (B) is obtained from Brevibacterium flavum chromosomal DNA library by cloning a DNA fragment that complicates serB deficiency of Escherichia coli as a open reading frame in the DNA fragment. (A) A protein which comprises an amino acid sequence of SEQ ID: 2 in Sequence Listing; or (B) A protein which comprises an amino acid sequence including substitution, deletion, insertion, addition or inversion of one or several amino acids in the amino acid sequence of SEQ ID NO: 2 in Sequence Listing, and which has phosphoserine phosphatase activity.