Disclosed is an agent for preventing muscular atrophy, which has an excellent preventive effect on muscular atrophy and comprises a whey protein hydrolysate.Specifically disclosed is an agent for preventing muscular atrophy, which comprises a whey protein hydrolysate, wherein the whey protein hydrolysate has a molecular weight distribution of 10 kDa or less (wherein the main peak appears at 200 Da to 3 kDa), an APL (average peptide chain length) of 2 to 8, a free amino acid content of 20% or less relative to the total amount of all of the constituents, a branched amino acid content of 20% or more, and antigenicity that is 1/100,000 or lower of the antigenicity of β-lactoglobulin.
