To make a system small in size and light in weight, to facilitate operation and to sufficiently cope with the densification of an image pickup element by constituting the system so that a third group becomes unmagnified when power variation from the wide end to the telescopic end is performed and a second group becomes unmagnified by the power variation.

This system is composed, in order from the object side, of a first group r3-r5 capable of adjusting the diopter from positive to negative and having a positive refractive power, a second group r6-r8 being a variator group for power variation and having a negative refractive power and a third group r9-r13 being a compensator lens group for making an image position fixed at the time of varying the power. The second group r6-r8 and the third group r9-r13 are changed around the unmagnification, respectively, by moving the second group r6-r8 from the object side to the image side and the third group r9-r13 from the image side to the object side, power variation from the wide end to the telephoto end is performed and the third group r9-r13 is made to be unmagnified complied with the unmagnification of the second group r6-r8.