PURPOSE: To obtain a lens that received a correction of aberration with high performance from the infinity to 1 magnification, by satisfying the prescribed conditions for a lens system of 3-group structure containing a positive lens, a negative combined meniscus lens and a positive lens put from the side of a subject.

CONSTITUTION: A lens system of 3-group structure contains a positive lens I, a negative combined meniscus lens II and a positive lens III put from the side of a subject. In such lens system, the distance between the 1st and 2nd groups is reduced with the distance increased between the 2nd and 3rd groups to perform the focusing from the infinity to a short distance. Furthermore the conditions of 9f≤f2 and 0.03f<d5<0.23f are satisfied, where the focal distance of the whole system is referred to as (f), the focal distance of the 2nd group is f2 and the distance between the 1st and 2nd group is d5 respectively. In such way, a lens that received a correction of aberration with high performance from the infinity to 1 magnification can be obtained.