Using betaKlotho or a substance that increases or inhibits betaKlotho activity as an agent for controlling the activity of FGF21 mediated by an FGF receptor, the present invention provides a pharmaceutical composition comprising such betaKlotho or such substance as an active ingredient, particularly, a pharmaceutical composition for anti-metabolic syndrome, and further particularly, a pharmaceutical composition for therapeutic or preventive use associated with the control of blood glucose level. In addition, the present invention provides a screening system for each of a substance that enhances or suppresses betaKlotho activity, an FGF21-like active substance, and a betaKlotho-like active substance, which uses a cell system that has expressed an FGF receptor and/or betaKlotho on the surface thereof.
