This is a ring-shaped part developed to detect the angle of mainly robot joints and enables angle information for the absolute angle to be outputted when using it in combination with a dedicated sensor. In addition to it having superior environment resistance when compared to optical type sensors, it also contributes to more compact devices since it is thin and lightweight. Furthermore, it is also easy to apply for robot joints due to its hollow shape which is large enough to allow cables and such items to pass through internally. Two types, a radial type and axial type, are available with different detection directions.