it may be detected as off track being occurred in some cases as described above the method for off track detection using only the tracking error signal may cause erroneous error due to a threshold value in consideration thereof in the example of fig1 the device operates as below so that no erroneous detection is caused and any off track can be detected without fail by referring to fig1 the example is described fig1 includes track zero cross detection means 21 wobble generation means 22 off track detection means 23 and off track determination means 24 the remaining means are the same as those in fig2 and thus are not described again described next is the brief summary of the operation of each block and the relationship among the blocks based on a signal provided by the optical detector 7 the tracking error signal generation means 11 generates a tracking error signal and forwards the resulting generated signal to all the tracking control signal generation means 12 the off track detection means 16 and the track zero cross detection means 21 as described above the off track detection means 16 detects any off track from the amplitude of the tracking error signal and forwards the result of the detection as a hi lo signal to the off track determination means 24 when the tracking error signal is.