An imaging lens includes a first lens group, a second lens group having positive refractive power, an aperture, and a third lens group having positive refractive power, sequentially disposed in that order from an object side to an image side. During a focusing from infinity to a short length, a combination of the second lens group, the aperture, and the third lens group as a single unit moves to the object side so as to reduce a distance to the first lens group. The second lens group includes four lenses of a second-first negative lens, a second-second positive lens, a second-third negative lens, and a second-fourth positive lens sequentially disposed in that order from the object side to the image side.