A lens optical system is disclosed. According to one embodiment of the present invention, a lens optical system, which has lenses sequentially arranged from an object side to an image side, may comprise: a first lens having positive refractive power and having an object-side surface convex toward the object side; a second lens having positive or negative refractive power; a third lens having positive or negative refractive power; and a fourth lens having negative refractive power and having an object-side surface concave toward the object side.