A zoom lens unit, including in order from an object side to an image side: a first lens group having a positive refracting power; a second lens group having a negative refracting power; a third lens group having a positive refracting power; and a fourth lens group having a positive refracting power, an aperture stop being disposed on an object side of the third lens group, wherein the third lens group has at least two positive lenses and one negative lens, wherein all the positive lenses of the third lens group satisfy the following formula: (1) −0.005865νd3p+0.93226