PURPOSE: To prevent the deterioration of an MTF by composing the title conversion circuit of a photoelectric conversion means receiving returned light from an optical recording medium and capable of photoelectrically converting returned light and an amplifying means converting currents obtained from the photoelectric conversion means into voltage and having a feedback resistor determining gains and constituting the feedback resistor of at least a plurality of resistors connected in series.

CONSTITUTION: An amplifier 3 composed of a detector 2 capable of photoelectrically converting light from an optical recording medium and an amplifier 3 converting photocurrent formed from the detector 2 into voltage is fed back through a feedback resistor 8, in which a resistor 5 having a capacitor 4 as a component and a resistor 7 having a capacitor 6 as a component are connected in series. Photocurrents formed by the detector 2 are converted into voltage by the amplifier 3 and the feedback resistor 8 at that time. Since the resistors 5 and 7 are connected in series, the value of combined resistance is doubled, and the value of combined capacitor is halved. Accordingly, the deterioration of an MTF defined by formula I can be prevented by simply reducing a capacitor component and without changing a resistance value.