PURPOSE: To improve an imaging property with a small number of lens elements and enables a higher variable power ratio by moving a specific lens group at the time of focusing and specifying a relation between the focal lengths and the back focus of a lens system and respective lens groups.

CONSTITUTION: A first group G1 consisting of a joined positive lens component L1 and a fifth group G5 having a negative refracting power move to an object side at the time of variable power from a wide angle end to a telephoto end. A second group consisting of a biconcave lens L21 and a positive meniscus lens L22 and a fourth group G4 consisting of a joined positive lens component L4 move to an object side at the time of focusing from a remote distance object to a short distance object. The focal lengths f1 to f4 of the respective groups G1 to G4, the focal lengths fw, ft over the entire part of the lens system at the wide angle end and the telephoto end and the back focuses Bfw Bft are so set as to satisfy the respective conditions 0.15<1f21/f1<0.5, 0.4<(Bf1-Bfw)/(ft-fw)<0.8-0.25<(f3-f4)/(f3+f4)<0.4.