The present invention addresses the problem of providing: an anti-GPR20 antibody that can be used to detect GPR20; a reagent for detecting GPR20 comprising said antibody; and a diagnostic reagent, test composition, etc., for a disease associated with expression of GPR20. Provided are: an antibody that binds specifically to a peptide comprising an amino acid sequence indicated by amino acids 1 through 48 in SEQ ID NO: 1, or an antigen-binding fragment of said antibody; a chimerized antibody, rabbitized antibody, etc., of said antibody; and a composition, etc., comprising said antibody.