As for a quadruple light receiving unit, in a case where divided regions of A to D as in a DPD scheme is defined, when binarization signals of light reception signals in regions A to D are set as signals A to D, exclusive OR between the signal A without delay and the signal B with delay, exclusive OR between the signal A with delay and the signal C without delay, exclusive OR between the signal B without delay and the signal D with delay, and exclusive OR between the signal B with delay and the signal D without delay are calculated, and a tracking error signal is obtained on the basis of the calculation of ( + )−( + ). Thus, the above problem can be solved.