A lens optical system includes first to fourth lenses that are sequentially arranged from an object, and which are between the object and an image sensor on which an image of the object is formed. The first lens has a positive refractive power and an incident surface that is convex toward the object. The second lens has a negative refractive power and both surfaces that are concave. The third lens has a positive refractive power and has a meniscus shape that is convex toward the image sensor. The fourth lens has a negative refractive power and at least one of an incident surface and an exit surface thereof is an aspherical surface. The lens optical system may satisfy an inequality that 0.5