In an optical scanning device for scanning both a high-density, HD, record carrier (38) and a low-density, LD, record carrier (18), a two-wavelength diode laser (50) is used for generating the HD scanning beam and the LD scanning beam. By arranging a composite diffraction element (60) close to the diode laser (50), which element has a first diffraction structure (63), for combining the HD beam and the LD beam, and a second diffraction structure (64), which acts as a lens for either the LD beam or the HD beam only, a compact device is obtained, which is suitable for writing the LD information layer (40).