PURPOSE: To prevent runaway of an optical head when track-crossing pulses are lost due to defects in a recording disk surface.

CONSTITUTION: When track-crossing pulses are lost, the level of an optical head speed signal 101 rapidly decreases. This decrease is detected by a band-pass filter 34 and a level comparator 35 to produce correcting pulses 113 from a supplementary pulse generator circuit 36 to correct the speed signal 101.