an illumination device , includes a secondary light source forming system having a deflecting member with a conical light deflecting surface for transforming received light into substantially ring - like light , the secondary light source forming system forming a ring - like secondary light source by using the ring - like light ; and an optical system for projecting divergent lights from portions of the secondary light source obliquely onto a surface to be illuminated so that the projected lights are superposed one upon another on the surface .