[Problem] To limit the occurrence of lateral chromatic aberration in an objective optical system, while widening the angle of view. [Solution] The following are arranged in order from the object side: a first lens group (G1) having a negative refractive power a stop (St) and a second lens group (G2) having a positive refractive power. The first lens group (G1) comprises, arranged in order from the object side: a first lens (L1) which is a negative single lens and a cemented lens (LS1) formed by cementing a positive lens and a negative lens, and having a negative refractive power. The second lens group (G2) comprises, arranged in order from the object side: a fourth lens (L4) which is a positive single lens and a cemented lens (LS2) formed by cementing a positive lens and a negative lens, and having a positive refractive power. The objective optical system is configured to satisfy conditional expression (1): 15.0
