An ultra wide angle imaging optical
system includes, in order from an object side, a first lens group, an aperture stop, and a second lens group. The first lens group includes, in order from the position closest to the object side, a negative
meniscus lens element convex to the object side, a negative lens element, and a negative lens element. The second lens group includes a plurality of positive lens elements. The first lens group and the second lens group each includes at least one anamorphic surface having different optical powers with respect to a first section extending in a first direction on a flat plane substantially orthogonal to an
optical axis, and with respect to a second section extending in a second direction substantially orthogonal to the first direction. The first lens group includes the lens element satisfying the following conditional formula (1):−0.6<(Ph−Pv)*(fh+fv)<−0.1 (1)wherePh: an
optical power in the first direction where a viewing angle is large;Pv: an
optical power in the second direction where the viewing angle is small;fh: a
focal length in the first direction with respect to the entirety of the optical
system; andfv: a
focal length in the second direction with respect to the entirety of the optical
system.