Patent ID: 7483181

Claim:
An optical reading unit, comprising: light radiating means for radiating light onto a recording medium; detecting means for detecting returning light from the optical recording medium to acquire a push-pull signal, wherein a light-receiving device being the detecting means has detection areas delimited by a plurality of parallel split lines, and wherein the position of one of the split lines is determined according to the position of a spot of the returning light on a light-receiving surface of the light-receiving device, and the push-pull signal is the difference between signals received on two detection areas delimited by said one of the split lines; split-line determining means for determining said one of the split lines as a detection reference line according to the position of the spot of the returning light on the light-receiving surface of the light-receiving device; and calculating means for performing a calculation based on signals acquired from the detection areas delimited by the split lines to acquire the push-pull signal.