in the compound rotary encoder of this invention , an absolute signal representing the upper m bits of a rotation angle signal , and an icreametal signal used for detecting the lower bits of the rotation angle signal are detected to obtain more detailed rotation angle information . moreover , the rotation angle obtained by counting the increamental signal closely matches that obtained from the absolute signal , assuring the detection of the rotation angle with high resolution and precision . since a rotating disk has only m bits of absolute code pattern , the rotary encoder can be small . this permits the absolute code pattern to have greater diametrical width so that a large output of the absolute signal can be stably obtained . on the other hand , the number of rotations can be obtained by counting and compensating a standard position signals . since the rotary disk has the patterns both for detecting the standard position signal and for detecting the rotation angle , this too allows the rotary encoder to be small .