To provide an endoscope objective optical system having a small F number, small size, and high imaging performance, and which is not prone to be affected by manufacturing errors. An endoscope objective optical system is configured from, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power, the first lens group G1 and third lens group G3 being fixed and the second lens group G2 moving during focusing on a close-distance object point, the third lens group G3 comprising a front group GF having positive refractive power and a rear group GR having positive refractive power, the front group GF and the rear group GR each being configured from one single lens or one cemented lens, and the conditional expressions (1-1) and (1-2) being satisfied. (1-1): 1 ≤ fG3f/fG3r ≤ 5； (1-2): 0.1 ≤ dG3fr/dG3r ≤ 1
