A photographing optical system includes seven 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, a fifth lens element, a sixth lens element and a seventh lens element. Each of the seven lens elements of the photographing optical system has an object-side surface facing toward the object side and an image-side surface facing toward the image side. The image-side surface of the second lens element is convex in a paraxial region thereof. The third lens element has negative refractive power. At least one lens element of the photographing optical system has at least one aspheric surface having at least one inflection point.