When a
wavelength of a first
laser beam with which a first recording medium including a first
recording layer is recorded and reproduced is indicated as λ1 (nm), a
wavelength of a second
laser beam with which a second recording medium including a second
recording layer is recorded and reproduced as λ2 (nm), the relationship between the
wavelength λ1 and the wavelength λ2 is set to be expressed by 10≦|λ1−λ2|≦120. The first
recording layer has a light
absorptance ratio of at least 1.0 with respect to the wavelength λ1. The light
transmittance of the first recording medium with respect to the wavelength λ2 is set to be at least 30 in both the cases where the recording layer is in a
crystal state and in an amorphous state. In order to
record and reproduce the optical multilayer disk with the above-mentioned characteristics, a multiwavelength
light source with the following configuration is used. Wavelengths of fundamental
waves with different wavelengths from injection parts formed at one end of a plurality of optical waveguides, which satisfy
phase matching conditions different from one another and are formed in the vicinity of the surface of a substrate, are converted simultaneously, and the first and second
laser beams are emitted from emission parts formed at substantially the same position at the other end of the optical waveguides. This enables an optimum optical
system for
high density recording and
reproduction to be obtained.