Provided is a protein synthesis promoter which has the effect of promoting the synthesis of protein. The protein synthesis promoter uses a whey protein hydrolysate having a molecular weight distribution of 10 kDa or less with a main peak in the range of 200 Da to 3 kDa, an average peptide chain length (APL) of 2 to 8, a free amino acid content of 20% or less and a branched-chain amino acid content of 20% or more relative to all of the constituent components, and an antigenicity of 1/100,000 or less compared to the antigenicity of beta-lactoglobulin.
