PURPOSE: To permit easy tracking during recording by making the magnetizing state on a recording track in the state of recording and erasing different from the magnetizing state on the guide tracks on both sides thereof.

CONSTITUTION: In an erasing state, a recording track 16a and guide tracks 16b, 16c differ in magnetization. To record, a beam is divided to a recording beam B and a tracking beam A by a grating 4. The beam A scans in front of the beam B across the tracks 16a and 16c. Since the magnetization 6a is in a different direction, the plane of polarization of the reflected light of the beam A differs. The polarization is converted to electricity with a photodetector 11. The above- mentioned signal which is converted to electricity is compared with a reference signal which is the electric signal corresponding to the output of the photodetector when the beam A scans the boundaries of the tracks, in a comparator 12. Since the quantity of incident light to the photodetector 11 changes when the beam A biases, the change is compared and the result is fed back to a tracking mechanism, whereby tracking servocontrol is executed.