An angle generator equipped with a self-calibration mechanism has been developed. Its angular span is more than 30°. The angular displacement of the axis of rotation is measured by an angle interferometer, which observes the displacement of two retro-reflectors attached to the rotation axis. The angle is calculated from the function of the observed interference order parameterized by the separation of the retro-reflectors and wavelength of the laser. To avoid the effects of long-term drift of the separation and wavelength due to a meteorological change, a self-calibration method is introduced. The self-calibration is realized by a 24-sided optical polygon attached to the axis through an indexing face gear with a 1° resolution. The autocollimator is calibrated by comparing its readings against angles set by the angle generator. Last year, a single-axis autocollimator calibration service was commenced using this system with an uncertainty of 0.1” and angular span of +-1000”.