Provided is a photographic lens optical system having low manufacturing costs and high performance. A lens optical system includes: first through fifth lenses, which are sequentially arranged along a light proceeding path between an object and an image sensor where an image of the object is formed; and an aperture provided between the object and the image sensor, wherein the first lens has positive refractive power, the second lens has negative refractive power and a flat incident surface, the third lens has positive refractive power and is convex towards the image sensor, the fourth lens has negative refractive power and is a meniscus lens convex towards the image sensor, the fifth lens has negative refractive power, wherein at least one of an incident surface and an emitting surface of the fifth lens is aspheric.