IMAGING OPTICAL SYSTEM AND IMAGING APPARATUS

To balance resolution between a center portion and a peripheral portion around an optical axis.SOLUTION: An imaging optical system 10 comprises, in order from an object side, a first lens group LG1, an aperture diaphragm S, and a second lens group LG2. The first lens group LG1 includes at least one aspherical lens AL having negative power. In the aspherical lens AL, a surface angle of an object-side surface has an extreme value between an optical axis Ax and an effective diameter position. The first lens group LG1 includes three or more lenses including a positive lens and a negative lens. The second lens group LG2 includes four or more lenses including a positive lens and a negative lens. A final lens closest to an image side in the second lens group LG2 has a convex object-side surface and a concave image-side surface. The imaging optical system 10 satisfies the following conditional expression: 3.0