A photographing lens system includes five lens elements which are, 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 third lens element has an object-side surface being convex in a paraxial region thereof. The fourth lens element has an object-side surface being convex in a paraxial region thereof.