An imaging lens includes an aperture stop, first, second, third, fourth and fifth lens elements arranged from an object side to an image side in the given order. The first lens element has a positive refractive power. The second lens element has an image-side surface with a concave portion in a vicinity of a periphery. The third lens element has an object-side surface with a concave portion in a vicinity of a periphery. The fourth lens element has an object-side surface with a convex portion in a vicinity of a optical axis. The fourth lens element and the fifth lens element have an image-side surface with a concave portion in a vicinity of a optical axis. The fifth lens element is made of a plastic material.