An optical system used in an imaging apparatus includes an optical element. In a case where the optical element is disposed on a magnification side with respect to an intersection point of an optical axis and a chief paraxial ray, the optical element is a negative lens, and in a case where the optical element is disposed on a reduction side with respect to the intersection point, the optical element is a positive lens. The optical element is configured to satisfy all of the following conditional expressions: 30≤νd≤40 1.225≤[nd−(14.387/νd)]≤1.276 0.4300≤[θgF−(2.9795/νd)]≤0.5010, where νd represents an Abbe number of the optical element, θgF is a partial dispersion ratio of the optical element for g-line and F-line, and nd is a refractive index of the optical element for d-line.