Once the encoder is assembled into the machine, the zero position of the input rotation axis is determined, and the zero position is always used as the origin of the coordinate, and the rotation angle is digitally output. There is no data disorder due to noise and other reasons, and there is no need to return to origin when starting. Moreover, even if the symbol cannot be read when rotating at a high speed, the correct data can be read by reducing the rotating speed. In addition, when a power outage is caused by a power outage or other reasons, the correct rotation data can still be read as long as the power is reconnected.