A compound optical unit has combined optical elements in which two optical elements having convex optical functional surfaces are joined to each other with the optical functional surfaces facing each other, the optical elements being formed of glass. An inner flange adjacent to the optical functional surfaces of each optical element is different in thickness from an outer flange formed outsides the inner flange, the outer flange has a top face formed higher then the optical functional surface, and each of the top faces of the outer flanges are jointed to each other.