An object of the present invention is to provide a bone strengthening agent which is effective in the prevention and treatment of osteoporosis, broken bones, rheumatism, arthritis, and other bone diseases, and to provide bone strengthening products such as food and beverages, feedstuff, and medicines containing the bone strengthening agent. The bone strengthening agent comprises, as active ingredients, a milk-derived basic protein fraction and/or a degradation product of a milk-derived basic protein fraction, and a whey protein hydosylate, and is effective in the prevention and treatment of various bone diseases including osteoporosis, broken bones, rheumatism, and arthritis.本發明之課題在於提供對於骨質疏鬆症與骨折、風濕症、關節炎等各種骨病的預防與治療有用的骨強化劑、及含有該骨強化劑的飲食品、飼料、醫藥等骨強化用製品。特徵在於含有乳源鹼性蛋白質組分(milk-derived basic protein fraction)及/或乳源鹼性蛋白質組分分解物與乳清蛋白水解物為有效成分的骨強化劑，對於骨質疏鬆症與骨折、風濕症、關節炎等各種骨病的預防與治療有用。
