An imaging 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, a fifth lens element and a sixth lens element. The first lens element has negative refractive power. The second lens element has an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof. The third lens element has positive refractive power. The fourth lens element has positive refractive power. The fifth lens element has negative refractive power. The sixth lens element has positive refractive power. The imaging optical lens system has a total of six lens elements.