Provided is an attachment for a denture which is difficult to have a fault if external force due to attachment and the like is applied. The attachment includes a convex element 10 that is a top structure of a natural tooth or an artificial tooth root 40 that is an anchor tooth, and a concave element 20 that is fixed to a position at a denture base 31, corresponding to the convex element. The convex element includes a fitting part 11, and a coupling part 12 that has a portion thinner than the fitting part and that couples the fitting part to the natural tooth or the artificial tooth root. The concave element includes a main body 21 of a tubular shape that has a bottom 21a at one end part thereof and an opening part 21b at another end part thereof, and in which a hollow portion 21c where the fitting part is inserted is formed, a groove 21e of an annular shape in an internal circumferential face of the main body in a direction of a circumference, an o-ring 22 whose outer circumferential portion is fit into the groove and whose inner diameter is smaller than the fitting part, and a discharge channel 21f that passes from the hollow portion through the groove, to communicate with an outside of the main body.
