An optical integrated unit includes a semiconductor laser (11), a polarized light beam splitter (14), a light receiving element (12), and a polarized light diffraction element (15) for diffracting an optical beam (20) and returning light. The polarized light diffraction element (15) is so provided as to receive the light beam (20) having passed through a polarized light beam splitter surface (14a), and as to diffract the returning light such that an optical path of the returning light is changed to lead to the light receiving element (12). This makes it possible to provide (i) an optical integrated unit in which the beam diameter of light incidenting on a diffraction element is large and in which an optical path length from the diffraction element to a light receiving element is long, and (ii) an optical pickup device including such an optical integrated unit.