The object of the present invention is to provide a catadioptric imaging system, or the like, which is capable of obtaining a desired image-side NA and an image circle without increasing the size of a reflecting mirror with a smaller number of lenses. This catadioptric imaging system comprises a first imaging optical system and a second imaging optical system, wherein the first imaging optical system is provided with a positive first lens group, an aperture stop, and a positive second lens group in the order from the object side, and the second imaging optical system is provided with a primary mirror comprising a concave first reflecting surface having a first radiation transmitting portion at the center thereof, and a secondary mirror comprising a second reflecting surface having a second radiation transmitting portion at the center thereof. In this case, all of the refracting members for constituting the optical system is formed of the same optical material, or at least one of the refracting surfaces and the reflecting surfaces is formed to be aspherical, or a refracting member is disposed to be separated from the first reflecting surface or the second reflecting surface.