To provide a therapeutic agent excellent in treatment or improvement of metabolic bone diseases such as osteoporosis caused by decrease of bone salt, having bone-improving action, rheumatism-improving action and periodontal disease-improving agent.

The present inventor discovered that limitin has bone-improving action, rheumatism-improving action and periodontal disease-improving action. The present invention provides a bone amount-improving and bone-strengthening agent, a rheumatism-improving agent and a periodontal disease-improving agent each containing limitin as an active ingredient.