PURPOSE: To prevent a data signal taken out from the cathode of a photodiode from being influenced by a tracking signal taken out from the anode by converting the detection current of an optical head to voltage only at a low band, by-passing a high frequency component and simultaneously converting it to voltage at a high band.

CONSTITUTION: A tracking signal inclusive of a data signal and a header signal is outputted by using the current from photodiodes 8a, 8b by a preamplifier 36. That is, the anode side of the diodes 8a, 8b are converted to current/voltage by a low speed amplifiers 52, 53 for making the tracking signal. Further, the signal from the cathode is supplied to the inverted input side of a high speed amplifier 51, converted to the voltage and becomes the header signal and the data signal. At this time, since the high frequency current flows to the diodes 8a, 8b by capacitors C1, C2, the high speed current is taken out by a high speed amplifier 51.