The present invention provides a method of screening an agonist or antagonist to a G protein-coupled receptor protein comprising the same or substantially the same amino acid sequence as the amino acid sequence represented by SEQ ID NO: 1, or a salt thereof, which comprises using the receptor protein or a salt thereof and the ligand or a salt thereof; etc. The present invention is useful for screening agents for the prevention/treatment of, e.g., leukopenia, leukemia, lymphoma, malignant tumor, ulcerative colitis, rheumatoid arthritis, inflammatory bowel disorders, tonsil disorders, collagen disease, inflammatory disease, leukocytosis, heart failure, inherited muscle disorders, muscular dystrophy, neuromuscular degenerative disease, myocardial infarction, obesity, mellitus diabetes, hyperlipemia, arteriosclerosis, metabolic syndrome, thrombocytopenia, thrombocytosis, cancer, pulmonary edema, multiple organ failure, etc.