An objective lens includes, in order from an object side, a front group having negative refractive power, an aperture stop AS, and a rear group having positive refractive power, wherein the front group includes, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex surface turned to the object side and a second lens L2 which is a negative lens with a concave surface turned to the object side the rear group includes, in order from the object side, a positive third lens L3 and a fourth lens L4 made up of a positive lens L4A and a negative lens L4B cemented together, and the objective lens satisfies conditional expression (1) below: -0.8 < f_F/f_R < -0.3 ... (1), where f_F is a focal length of the front group, and f_R is a focal length of the rear group.
