A therapeutic agent for periodontal disease that is effective against bacteria inducing periodontal disease and promotes regeneration of alveolar bone, which therapeutic agent is based on a material of scollop shell and can realize appropriate prevention and treatment of periodontal disease. The desired therapeutic agent for periodontal disease is obtained from an aqueous solution resulting from dissolution in water of a mixture of calcium carbonate powder produced by primary firing of a pulverizate of shells involving a body of crystal structure according to calcite type structure of calcium carbonate with calcium oxide powder produced by firing the calcium carbonate powder from the shells at temperature higher than at the primary firing.
