A long-acting improver of muscular fatigue characterized by comprising 4 kinds of amino acids made up of leucine, isoleucine, valine and glutamine, and a whey protein component (whey protein and/or decomposition product of whey protein). At least one of a whey protein isolate (WPI), a whey protein concentrate (WPC), β-lactoglobulin, and α-lactalbumin is used as the whey protein. Novel food or drink, and pharmaceuticals which exhibit sustained recovery effects on muscular fatigue are provided.