585093 Provided is a milk protein fraction derived from milk, wherein the milk protein fraction contains proteins having a molecular weight of 12,000 to 16,000 daltons determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), contains 18 to 20wt% of basic amino acids in the constituent amino acid composition, has a basic amino acid/acidic amino acid ratio of 0.7 to 0.9, and has an osteoclastogenesis inhibitory effect.