A centering device for centrally chucking a rotary tool includes a socket on a mandrel of a tool holder. A tool arrangement includes a tool holder that has a mandrel, and including a rotary tool that is placed on the tool holder and includes a socket. In order to create a universal centering device that is easy to manufacture and can be used for a multitude of internal chucking units, and create a tool arrangement in which the rotary tool can be centered with high accuracy on the internal chucking unit, the centering device is designed as a closed centering ring which can be inserted between the rotary tool and the mandrel and which has an elastically deformable contour, and such a centering device is disposed between the mandrel and the rotary tool in the tool arrangement.