An objective lens for endoscopes includes, in order from the object side: a front group; an aperture stop; and a positive rear group. The front group includes, in order from the object side, a negative first lens, in which the absolute value of the radius of curvature of the surface toward the image side is less than that of the surface toward the object side, and at least one plane parallel plate. The rear group includes, in order from the object side, a positive second lens, and a cemented lens formed by a positive third lens and a negative fourth lens. The coupling surface of the cemented lens is convex toward the image side. Conditional Formulae (1) through (3) concerning the plane parallel plates within the front group, the focal length of the first lens, the radius of curvature of the coupling surface of the cemented lens, etc., are satisfied.