The object of the present invention is to provide a method for screening a substance involved in a metabolic shift of skeletal muscle, and a kit for screening a substance involved in a metabolic shift of skeletal muscle.The object can be solved by a muscle stem cell or myoblast comprising at least one myosin-heavy chain fusion gene selected from the group consisting of a myosin-heavy chain I fusion gene wherein a myosin-heavy chain I gene and a fluorescent protein or photoprotein gene are fused, a myosin-heavy chain IIa fusion gene wherein a myosin-heavy chain IIa gene and a fluorescent protein or photoprotein gene are fused, a myosin-heavy chain IId/x fusion gene wherein a myosin-heavy chain IId/x gene and a fluorescent protein or photoprotein gene are fused, and a myosin-heavy chain IIb fusion gene wherein a myosin-heavy chain IIb gene and a fluorescent protein or photoprotein gene are fused.