An agent for periodontal disease includes, as an active component, a methanebisphosphonic acid derivative or a hydrate thereof represented by the general formula (I): [wherein X, Y, m, n, The methanebisphosphonic acid derivative represented by the general formula (I) or a hydrate thereof according to the present invention has activities such as inhibitory effect on cell infiltration to the affected part associated with periodontal disease, and is useful for the prophylaxis or treatment of periodontal disease.