Using one optical element on which diffraction gratings for diffracting two laser beams each having a different wavelength are formed at both surfaces, the first laser beam and the second laser beam outputted from two semiconductor lasers are made to converge on an optical disc by use of the same optical system. Directions of the grating grooves of the first diffraction grating and the second diffraction grating are set in a manner so that the direction in which a straight line binding +1.sup.st-order, 0.sup.th-order and -1.sup.st-order diffracted lights of the first laser beam diffracted by the first diffraction grating intersects tracks on the optical disc belongs to an opposite side to the direction in which a straight line binding +1.sup.st-order, 0.sup.th-order, and -1.sup.st-order diffracted lights of the second laser beam diffracted by the second diffraction grating intersects the tracks.