An absolute rotary encoder comprises a scale (SCL) having marks arranged at a first pitch; a first detector (PDA_A) and a second detector (PDA_B) including plural photoelectric conversion elements arranged at a second pitch smaller than the first pitch, and configured to detect a predetermined number of marks, the second detector disposed opposite to the first detector; and a computing device (CULC). The computing device is configured to generate a data string by quantizing a periodic signal output from the first detector, and obtains first angle data from the data string, to normalize amplitudes of the periodic signals output from the first and second detectors, to average the normalized periodic signal to obtain second angle data from a phase of the averaged periodic signal, and to combine the first and second angle data to generate data representing an absolute rotation angle.