A flux separating unit is maintained in a stable state with a high positioning accuracy relative to a physical deformation when the light flux separating unit is attached or a great temperature change after the light flux separating unit is attached, in an optical pickup device including in a casing a projection optical system, a light receiving optical system and the parallel flat plate shaped light flux separating unit that separates a light flux advancing in the light receiving optical system from a light flux advancing in the projection optical system.