PURPOSE: To satisfactorily reproduce data from a magneto-optical disk which has a high density recording with an improved line density.

CONSTITUTION: Recording data Din is recorded on a magneto-optical disk 100 by a preencoder 4 in a magnetic field modulation system as NRZI data while intermittently radiating a laser. Reproduced RF signals from the disk 100 are clamped for each segment by a clamping circuit 13, converted into digital signals by an A/D converter 14 and supplied to a data detecting circuit 17 after waveforms are equalized so as to close the shape of a cos filter suitable for partial response PR (1, 1) by an equalizer 15. In the data detecting circuit 17, a data detection of PR (1, 1) is implemented employing the viterbi algorithm to obtain regenerative data Dout (NRZ data). Since PR (1, 1), which possitively uses intercode interference, is applied, an enough phase margin is secured even though a high density recording with an increased line density is conducted. Furthermore, a coding error rate is reduced because a Viterbi decoding is applied and S/N is improved.