switch 10 adapted for switching between engagement and disengagement of the tracking servo on the other hand the output signal of a tracking servo circuit 6 is routed to a fixed contact 10 b on the engaging side of the servo engaging disengaging switch 10 a signal obtained at a movable contact 10 a of the servo engaging disengaging switch 10 is sent via a tracking drive circuit 11 to the optical pickup 4 to control the objective lens 4 e and hence the trajectory of the light beam 4 b a display device 12 demonstrates the calculated results otherwise the configuration shown in fig1 is formed similarly to that of a conventional optical disc player the operation of crosstalk measurement is explained by referring to fig4 to 7 in the present embodiment in measuring the crosstalk of the optical disc 1 the crosstalks of an inner rim area 1 b a mid area 1 c and an outer rim area 1 d are measured as shown in fig7 the crosstalks at the inner rim area 1 b mid area 1 c and at the outer rim area 1 d are measured in similar manner alternatively the crosstalk may also be measured over the entire areas of the optical disc 1 in measuring the crosstalk of the optical disc 1 the movable contact 10 a of the servo engaging.