An imaging lens system includes seven lens elements. The seven lens elements 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. The first lens element with positive refractive power has an object-side surface being convex in a paraxial region thereof. The second lens element with negative refractive power has an object-side surface being concave in a paraxial region thereof. The sixth lens element has positive refractive power. The seventh lens element has an image-side surface being concave in a paraxial region thereof, and the image-side surface of the seventh lens element has at least one inflection point in an off-axis region thereof.