A photographing optical lens system includes, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element and a fifth lens element. The first lens element has positive refractive power. The second lens element has negative refractive power. The fourth lens element with negative refractive power has an object-side surface being convex and an image-side surface being concave in a paraxial region thereof, wherein, either the object-side surface thereof, the image-side surface thereof or both the two surfaces thereof have at least one critical point in an off-axial region thereof, and either the object-side surface thereof, the image-side surface thereof or both the two surfaces thereof are aspheric.