In a test for supporting diagnosis of periodontal disease, a test method, whose measurement result has reproducibility and can be an objective index, is achieved and the loss of a tooth is predicted by use of the obtained objective index. A periodontal disease diagnosis supporting device supports diagnosis of periodontal disease by use of a captured three-dimensional image of a tooth part. The device includes a tooth root adhesion degree measuring part for measuring a degree of adhesion between a tooth root and alveolar bone by use of the image. The device further includes a periodontal disease diagnosis supporting part for supporting diagnosis of periodontal disease by use of a measurement result of the measuring part.