An optical bench, an integrated optical system, and an optical alignment method are provided. The integrated optical system includes a light source; a main photodetector which receives light that is emitted from the light source and reflected from a disc; an optical bench on which the light source and the main photodetector are installed; a lens unit installed on the optical bench; and an optical path separator which separates a path of light from the light source to the lens unit and a path of light from the lens unit. The optical bench includes a landing recess which is open upward toward the disc and which has an aperture on a bottom thereof to pass light. The optical path separator is mounted within the landing recess.