To make it possible to adequately digitalize RF signals by setting a regulation level at the optimum level of the RF signals regardless of whether tracking is adequately executed or not and controlling the gain of the RF signals.

A controller 20 sets a changeover switch 17 at a terminal (b) side when the top position of data is not detectable right after reproduction. An S/H circuit 16 sample-holds the average value of the levels of the RF signals from a voltage control circuit 11 according to the sample pulses from a pulse generating circuit 19. A difference detecting circuit 18 detects the difference between the level of the RF signals supplied from the changeover switch 17 and the reference level and controls the voltage control circuit 11 so as to regulate the level of the RF signals in such a manner that the difference is made zero.