An imaging lens includes: a first lens element having a positive refracting power, and having a convex object-side surface facing toward an object side; a second lens element having a negative refracting power, and having a concave image-side surface facing toward an image side; a third lens element having a negative refracting power; a fourth lens having a convex image-side surface facing toward the image side; and a fifth lens element having an image-side surface with concave and convex portions and facing toward the image side. Absolute value of a difference between Abbe numbers of the second and third lens elements is less than 10. A quotient of a thickness of the fourth lens element divided by a sum of widths of air gap among the lens elements ranges between 0.5 and 1.