There is provided a tool for friction stir welding, which is capable of promoting temperature rise of materials to be joined during joining to achieve friction stir welding in a short time, is excellent in heat insulating property of a coating layer, and is excellent in oxidation resistance and wear resistance. A tool for friction stir welding according to the present invention is a tool for friction stir welding including a base material and a coating layer formed on the base material, wherein the coating layer is formed of one or more layers, and at least one layer of the coating layer has a thermal permeability of 5000 J/s0.5·m2·K or less.