Disk apparatus

An AC amplifying circuit is AC coupled through capacitors to a current/voltage converting circuit for converting a photosensitive current of a reproduction light from an optical disk medium to a voltage signal and for outputting as differential signals. A transient absorbing circuit compares reproduction voltages of the differential signals outputted from the AC amplifying circuit and controls charge and discharge of the capacitors on the basis of comparison outputs so that both of the reproduction voltages coincide with an AC ground, thereby automatically absorbing a transient state.