A wide-angle optical system includes a first group having negative and positive lenses, a second group having a catadioptric optical element, and a third group. The catadioptric optical element includes a first surface at an object side, a second surface at an image side, and a third surface. The first surface has a first transmission surface and a first reflection surface disposed therearound. The second surface has a second transmission surface and a second reflection surface disposed therearound. The third surface is a circular conical transmission surface that is disposed between the first surface and the second surface and an apex of which is located at the object side.