The present invention provides a polypeptide selected from the following (A), (B) and (C), having a function or an activity as a receptor of an eicosanoid (5-oxo-ETE, etc.); (A) a polypeptide comprising an amino acid sequence shown by SEQ ID NO:2 or SEQ ID NO:21; (B) a polypeptide comprising an amino acid sequence shown by SEQ ID NO: 2 or SEQ.ID.NO:21 in which one or several amino acids are deleted, substituted or added; (C) a polypeptide encoded by a nucleic acid which hybridizes under stringent condition with a nucleic acid comprising a nucleotide sequence shown by SEQ ID NO:1 or SEQ ID NO:20 or a complement thereof, a nucleic acid encoding the polypeptide, a recombinant vector and a host cell comprising the same, a method for detecting a function or an activity of the polypeptide using the same, and a method for screening or identifying a ligand or an effector (an agonist or an antagonist) of the polypeptide using the same, a pharmaceutical composition comprising an antagonist of the polypeptide, and a therapeutic method using the antagonist, etc.