A 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 with negative refractive power has a concave image-side surface in a paraxial region. The second lens element with refractive power has a convex object-side surface in a paraxial region. The third lens element has positive refractive power. The fourth lens element with positive refractive power has an object-side and an image-side surfaces being aspheric. The fifth lens element with negative refractive power has an aspheric concave object-side surface and an aspheric convex image-side surface in a paraxial region. The sixth lens element with refractive power has an image-side surface being concave in a paraxial region with a convex shape in an off-axis region.