Excellent aberration correction, suitability for high-definition and high-pixel solid state imaging elements, a small outer diameter of an end and reduction in manufacturing cost are achieved. A wide-angle objective optical system includes, in order from an object side to an image side: a first lens group (G1)； and a second lens group (G2) having positive refractive power. The first lens group includes, in order from the object side to the image side: a first lens (L1) having negative refractive power； a second lens (L2) having a concave face as an object-side face and having negative refractive power； a brightness diaphragm (S)； and a third lens (L3) having positive refractive power. The following condition expressions are satisfied: - 0.5 <； f / f 1 <； 0.5 0.3 <； f / f 2 <； 0.7 wherein f1, f2 and f are focal distances of the first lens group, the second lens group, and the entire wide-angle objective optical system, respectively.
