An optical system includes a first lens including a positive refractive power, a second lens including a positive refractive power and a convex image-side surface, a third lens, and a fourth lens. The optical system includes a fifth lens including a concave object-side surface and a concave image-side surface, and a sixth lens including an inflection point formed on an image-side surface thereof. The first to sixth lenses are sequentially disposed from an object toward an imaging plane.