To provide an objective lens by which a microscope main body can be miniaturized and simplified and which has high precision, hardly generates insufficiency of marginal light quantity and can change a focus position and to provide an automatic focusing microscope using the same.

The automatic focusing microscope is constituted of a positive first lens group G1 and a second lens group G2 in order from a sample side, the first lens group G1 is movably disposed along an optical axis direction and the focus position can be changed by moving the first lens group G1 and the microscope is distinguished by satisfying following conditional formulae (1), (2). 0.5<f1/f>10...(1) f2/f>1.9...(2) wherein f1 is the focus distance of the first lens group, f2 is the focus distance of the second lens group and (f) is the focus distance of the objective lens.