A skin-whitening agent offering an excellent whitening effect and being effective in preventing and treating age spots, freckles, etc., where such skin-whitening agent contains as its effective ingredient a whey protein hydrolyzate characterized by a molecular weight distribution of 10 kDa or less, main peak of 200 Da to 3 kDa, APL (average peptide-chain length) of 2 to 8, free amino acid content of 20% or less, and antigenicity of one-ten thousandth of β-lactoglobulin or less, as well as a cosmetic, drink or food, feed, pharmaceutical preparation or other skin-whitening product containing such skin-whitening agent.
