An extract of Citrus depressa, preferably an organic solvent extract of a fruit and/or leaf of Citrus depressa, a supercritical extract of a fruit and/or leaf of Citrus depressa, or a subcritical extract of a fruit and/or leaf of Citrus depressa, containing 0.3 mass % or more of a polymethoxyflavonoid in terms of solid matter, for example, 0.2 mass % or more of nobiletin and/or 0.1 mass % or more of tangeretin in terms of solid matter, or a polymethoxyflavonoid, such as nobiletin and tangeretin, is used as an active ingredient of a muscle atrophy inhibitor.
