The present invention provides a novel secretory/membrane protein associated with adipocyte differentiation and/or metabolism function, specifically, an adipocyte-derived secretory/membrane protein containing amino acid sequence which is the same or substantially the same as an amino acid sequence represented by SEQ ID NOS: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 or 22, a nucleic acid encoding it, an antibody therefor, a method of screening prophylactic and/or therapeutic agents for diseases involving abnormality of adipocyte differentiation/metabolism function using it and/or a kit for the screening, a prophylactic and/or therapeutic agent for the diseases or a diagnostic agent containing the membrane protein.