An imaging lens system comprising: a first lens group having positive refractive power; a stop; a second lens group having positive refractive power; and a third lens group having one of positive refractive power and negative refractive power, disposed directly in that order from an object side to an image side, the first lens group consisting of a first-group-first positive lens and a first-group-second negative lens, disposed directly in that order from the object side to the image side, the third lens group including a third-group-first negative lens and a third-group-second positive lens, disposed directly in that order from the object side to the image side, a combination of the first lens group and the second lens group moving together as a single unit to the object side in focusing from infinity to a close distance to increase a distance between the second lens group and the third lens group, conditional expression below being satisfied: 0.40 < dL 31 − L 32 / L 3 g < 0.75 where dL31-L32 denotes air spacing between the third-group-first negative lens and the third-group-second positive lens in the third lens group, and L3g denotes a distance along the optical axis between an object-side surface of the third-group-first negative lens and an image-side surface of the third-group-second positive lens, wherein conditional expressions and below are satisfied: 55.0 < ν dn < 95.0 − 5.0 < ν dn − ν dp < 15.0 where vdp denotes the Abbe number of material of the first-group-first positive lens with respect to the d-line, and vdn denotes the Abbe number of material of the first-group-second negative lens with respect to the d-line, and wherein conditional expression below is satisfied: − 0.80 < fL 11 / fL 12 < − 0.60 where fL11 denotes a focal length of the first-group first positive lens, and fL12 denotes a focal length of the first-group-second negative lens. a first lens group having positive refractive power; a stop; a second lens group having positive refractive power; and a third lens group having one of positive refractive power and negative refractive power, disposed directly in that order from an object side to an image side, the first lens group consisting of a first-group-first positive lens and a first-group-second negative lens, disposed directly in that order from the object side to the image side, the third lens group including a third-group-first negative lens and a third-group-second positive lens, disposed directly in that order from the object side to the image side, a combination of the first lens group and the second lens group moving together as a single unit to the object side in focusing from infinity to a close distance to increase a distance between the second lens group and the third lens group, conditional expression below being satisfied: 0.40 < dL 31 − L 32 / L 3 g < 0.75 where dL31-L32 denotes air spacing between the third-group-first negative lens and the third-group-second positive lens in the third lens group, and L3g denotes a distance along the optical axis between an object-side surface of the third-group-first negative lens and an image-side surface of the third-group-second positive lens, wherein conditional expressions and below are satisfied: 55.0 < ν dn < 95.0 − 5.0 < ν dn − ν dp < 15.0 where vdp denotes the Abbe number of material of the first-group-first positive lens with respect to the d-line, and vdn denotes the Abbe number of material of the first-group-second negative lens with respect to the d-line, and wherein conditional expression below is satisfied: − 0.80 < fL 11 / fL 12 < − 0.60 where fL11 denotes a focal length of the first-group first positive lens, and fL12 denotes a focal length of the first-group-second negative lens.