Endoscope objective optical system

Provided is a small endoscope objective optical system that allows stereoscopic viewing even though a wide angle is used, that reduces the F-number, and that also reduces vignetting. Provided is an endoscope objective optical system that consists of, sequentially from the object side, a negative first lens group (G1), a positive second lens group (G2), and a pair of third lens groups (G3) that are disposed side-by-side in the direction of parallax and that form two optical images with parallax, wherein aperture stops (S) are individually provided in the third lens groups, and conditional expression (1) below is satisfied: Fob_n / Fob_p > ˆ’ 0.5 where Fob_n is a focal length of the first lens group, and Fob_p is a focal length of the second lens group.