Disclosed is: an antibody directed against FGF23; and a pharmaceutical composition (e.g., a prophylactic or therapeutic agent) for a disease which can be prevented or treated by inhibiting the activity of FGF23 by using the antibody. Specifically disclosed is an antibody directed against human FGF23 which is produced by hybridoma C10 (Accession Number: FERM BP-10772) or a functional fragment of the antibody.