To obtain a relatively compact extender optical system in which the aberration of a single body is minimized and the aberration is made less likely to affect various aberrations even when it is mounted in a main lens.

The rear converter lens includes, in order from the object side, a first lens group G1 having a negative focal distance, a second lens group G2 having a positive focal distance, and a third lens group G3 having a negative focal distance. The first lens group G1 is composed of, for example, a cemented lens of a negative lens L1 whose image side face is concave and a positive lens L2 of a positive meniscus shape whose object side face is convex, arranged in that order from the object side.