An imaging lens includes a first lens group and a second lens group arranged in this order from an object side to an image plane side. The first lens group includes a first lens having positive refractive power, a second lens having negative refractive power, and a third lens, arranged with a space in between. The second lens group includes a front side lens group having negative refractive power and a rear side lens group having positive refractive power. The front side lens group includes a fourth lens and a fifth lens arranged with a space in between. The rear side lens group includes a sixth lens and a seventh lens arranged with a space in between. The fourth lens is formed in a shape so that a surface thereof on the object side has a specific curvature radius so that a specific conditional expression is satisfied.