Abstract: An objective includes a first lens group that has a positive refractive power and a second lens group that has a negative refractive power. The objective includes a first negative lens and satisfies 0.005?do1/ho1?0.1??(1) 0.005?hmin/hl?0.72??(2) 10 mm?L?100 mm??(3) 0.1?L/f?31??(4) when do1 is a thickness of the first negative lens, ho1 is an axial marginal ray height on a lens surface on the object side of the first negative lens, hmin is a minimum value of an axial marginal ray height in the second lens group, hl is a height of an axial marginal ray on a lens surface of the objective that is situated closest to the image side, L is a length of the objective, and f is a focal length of the objective.