Abstract: A positional information generating apparatus comprises a code disposed on a main track on which M-sequence codes form a cyclic code of different code words, and sensors disposed for attaining relative movement with reference to a direction of the main track. The code word is detected from the main track by the sensors for generating positional information. A sensor array for the main track in which a greater number of sensors than the number of elements of a code word are disposed over a span corresponding to a length of one code word in such a way that at least one sensor is located on each code element to define a code word to be read. A relative position detector is provided for detecting a relative positional relationship between the sensor array for the main track and the main track.