The present invention is an optical device for diffracting an incident light by a hologram element(19) and receiving the light in light receiving areas(20A to 29) on a light receiving element(12). The light receiving element(12) receives a reflected light of a main beam used for reading information from an optical disc and a reflected light of a sub beam used for tracking operation in respective independent light receiving areas, and receives the reflected light of the main beam in a common light receiving area regardless of the wavelength values and receives the reflected light of the sub beam in different light receiving areas depending on the wavelength values. Thus, when recording and/or reproducing an information signal onto/from an optical disc using different wavelength values of the light source such as 'DVD' and 'CD', it is possible to eliminate the affect from an unnecessary reflected light from the optical disc and eliminate complexity of operation about the output signal. |