PURPOSE: To attain stable tracking control at recording/rproduction of picture information by irradiating a sub-beam between tracks and detecting the reflected light so as to decrease the level change in the reflected light between tracks having no shape change.

CONSTITUTION: In a laser light from a semiconductor laser 11, a main beam 20 has a high output so as to form pits and a sub beam 21 has a low output not formed with a pit at recording of information, and the main beam 20 and the sub beam 21 have a low output at reproduction by splitting the laser beam at a diffraction grating 13, the main beam 20 is irradiated on a track T on the disc 16 via a polarized beam splitter 14 and the sub beam 21 is irradiated between the tracks T. The reflected light of the sub-beam 21 is led to a photoelectric converter 23 having photodetectors 23a, 23b and the tracking control to the track T is attained by using an output Y of a differential amplifier 24. The reflected light of the main beam 20 is detected by a photoelectric converter 22 and an information read signal X is outputted to an information processing section 10.