PURPOSE: To precisely learn a read error when it occurs by permitting a cross track number detection part to detect the number of cross tracks at the time of track access.

CONSTITUTION: An analog signal from an optical disk, which is read from a servo area, is supplied to a binarization shaping circuit 22. It shapes the analog signal into a bianary signal and it is outputted to the cross track number detection part 25 and a memory 24. It receives the output of the binarization shaping circuit and stores the pattern of a part fitted to the access mark in accordance with the signal of a read error judgement part 33 which is to be mentioned hereafter. The cross track number detection circuit 25 receives the outputs of the binarization shaping circuit 22 and the memory 24, compares the two patterns of the part of the access mark and calculates the number of the tracks (number of cross tracks) where reproduced light beams are crossed.