A first lens group in a reflex, magnifying optical system includes sequentially from the side of an object, a first lens that has a negative refractive power and is a meniscus lens having a concave aspect facing toward an image, an optical element (prism) that refracts an optical path, a second lens having a negative refractive power and a concave aspect facing toward the object, and a third lens having a positive refractive power. A portion of an image-side aspect of the first lens abuts a plane of incidence of the optical element. A portion of an object-side aspect of the second lens abuts a plane of transmission of the optical element.