The present optical semiconductor device includes a semiconductor laser, an optical block provided with a hologram element for diffracting a laser beam that has been emitted from the semiconductor laser and reflected by a disk, a photo-detector for receiving the laser beam diffracted by the hologram element and outputting an electric signal, and a package for receiving the semiconductor laser and the photo-detector. An internal space of the package has a plurality of independent spaces, and the semiconductor laser and the photo-detector respectively are received in the spaces that are different from each other. With this configuration, it is possible to achieve an optical semiconductor device that can be made smaller and thinner and has a highly-reliable semiconductor laser element.