A lens system for imaging consisting, in order from an object side , of a first lens group (G1) that has negative refractive power, a second lens group (G2) that has positive refractive power, a third lens group (G3) that has positive refractive power, a stop (St), and a fourth lens group (G4) that has positive refractive power, wherein, during focusing, the second lens group (G2) and the third lens group (G3) move independently along the optical axis , and during focusing from infinity to a closest distance, a distance between the first lens group (G1) and the second lens group (G2) along an optical axis increases, a distance between the second lens group (G2) and the third lens group (G3) along the optical axis decreases, and the fourth lens group (G4) and the stop (St) disposed on the object side of the fourth lens group (G4) are fixed with respect to the image plane , the third lens group (G3) includes, at a position closest to an image plane side , a cemented lens (B2) disposed on the object side of the stop (St) and including an image plane side-surface (S16) with a surface that is concave, the fourth lens group (G4) includes, at a position closest to the object side , a cemented lens (B3) disposed closest to the image plane side of the stop (St) and including an object side surface (S18) with a surface that is concave, the cemented lens (B2) disposed on the object side of the stop (St) and the cemented lens (B3) disposed on the image plane side of the stop (St) have negative refractive powers, and a radius of curvature g3er (r16) of the image plane side-surface (S16) that is concave, the radius of curvature g4fr of the object side surface (S18) that is concave, a focal length B2f of the cemented lens (B2) disposed on the object side of the stop (St), and a focal length B3f of the cemented lens (B3) disposed on the image plane side of the stop (St) satisfy following conditions. 2.5 ≤ g 4 fr / g 3 er ≤ 4.0 1.7 ≤ B3f / B2f ≤ 3.0 . wherein, during focusing, the second lens group (G2) and the third lens group (G3) move independently along the optical axis , and during focusing from infinity to a closest distance, a distance between the first lens group (G1) and the second lens group (G2) along an optical axis increases, a distance between the second lens group (G2) and the third lens group (G3) along the optical axis decreases, and the fourth lens group (G4) and the stop (St) disposed on the object side of the fourth lens group (G4) are fixed with respect to the image plane , the third lens group (G3) includes, at a position closest to an image plane side , a cemented lens (B2) disposed on the object side of the stop (St) and including an image plane side-surface (S16) with a surface that is concave, the fourth lens group (G4) includes, at a position closest to the object side , a cemented lens (B3) disposed closest to the image plane side of the stop (St) and including an object side surface (S18) with a surface that is concave, the cemented lens (B2) disposed on the object side of the stop (St) and the cemented lens (B3) disposed on the image plane side of the stop (St) have negative refractive powers, and a radius of curvature g3er (r16) of the image plane side-surface (S16) that is concave, the radius of curvature g4fr of the object side surface (S18) that is concave, a focal length B2f of the cemented lens (B2) disposed on the object side of the stop (St), and a focal length B3f of the cemented lens (B3) disposed on the image plane side of the stop (St) satisfy following conditions. 2.5 ≤ g 4 fr / g 3 er ≤ 4.0 1.7 ≤ B3f / B2f ≤ 3.0 . <EOS>