A monolithic double-wavelength semiconductor laser diode is provided in a DVD/CD
compatible player to suppress deterioration in the optical characteristics of a
reading light spot. A laser diode is a monolithic element which has two light emitting
points on a single substrate for emitting two different laser beams having different
wavelengths with each other. A central line of a main laser beam for use in reproducing
DVDs is positioned closer to the optical axis Y of an optical system than a central
line of a laser beam for use in reproducing CDs. In another arrangement, the central
line of a main laser beam for use in reproducing DVDs is positioned so as to be
coincident with the optical axis Y of the optical system.