IMAGING OPTICAL SYSTEM AND IMAGING DEVICE

To provide an imaging optical system and an imaging device that are wide-angle and compact and are easy to manufacture.SOLUTION: An imaging optical system (10) comprises, in order from the object side, a front group LF, an aperture stop S, and a rear group LB. The front group LF includes a first lens L1 having negative refractive power. The rear group LB includes a fourth lens L4 that is located on the most object side and has positive refractive power, and a seventh lens L7 that is located on the most image side and has negative refractive power, the image-side plane having an extreme value at positions other than the intersection with the optical axis. The imaging optical system (10) satisfies the conditional expression below. Expression (1): 0.6