An object is to provide an attachment for a denture which is difficult to have a fault if external force is applied. The attachment includes a convex element that is a top structure of an anchor tooth or an artificial tooth root, and a concave element that is fixed to a denture base. The convex element includes a fitting part and a coupling part that couples the fitting part to a natural tooth or the artificial tooth root. The concave element includes a main body in which a hollow portion where the fitting part is inserted is formed, a groove in an internal circumferential face of the main body in a direction of a circumference, an o-ring that is fit into the groove and whose inner diameter is smaller than the fitting part, and a discharge channel via which the hollow portion and an outside communicate.
