In order to provide a novel fluorescent protein and use thereof, the polypeptide according to the present invention has fluorescent properties in the presence of bilirubin and includes (1) the amino acid sequence of SEQ ID NO: 1, (2) an amino acid sequence having, for example, substitution of 1 to 21 amine acids in the amino acid sequence of SEQ ID NO: 1, (3) an amino acid sequence having 85% or more sequence identity to the amino acid sequence of SEQ ID NO: 1, or (4) the amino acid sequence encoded by a polynucleotide that hybridizes with a polynucleotide consisting of a sequence complementary to the polynucleotide encoding the polypeptide according to the amino acid sequence in (1) under a stringent condition.