An endoscope optical system, including a front group and a rear group arranged in this order from an object side such that an aperture stop is arranged between the front and rear groups, wherein the front group includes a negative lens and a positive lens arranged in this order from the object side, the rear group includes a positive lens and a cemented lens arranged in this order from the object side, and when f (unit: mm) denotes a focal length of an entire endoscope optical system, EX (unit: mm) denotes a distance (which takes a minus sign on the object side with respect to an image plane) from the image plane to an exit pupil, and f2 (unit: mm) denotes a focal length of the rear group, the endoscope optical system satisfies conditions:−10<；EX/f<；−6 (1),and1.15<；f2/f<；1.35 (2).
