The present invention relates to an optical system. An optical system of the present invention includes a first lens having a positive refractive power and an object-side surface convex toward an object side; a second lens having a negative refractive power and an image-side surface concave toward an image side; a third lens having a negative refractive power; a fourth lens having a positive refractive power; a fifth lens having a positive refractive power and an image-side surface convex toward the image side; and a six lens having a negative refractive power and an image-side surface concave toward the image side.
