An interference objective lens includes: an objective lens configured to converge a light to be emitted from a light source toward a measurement target; a reference surface unit having a reference surface; and a beam splitter configured to split the light having passed through the objective lens into a reference optical path facing toward the reference surface and a measurement optical path facing toward the measurement target, to synthesize a reflected light from the reference surface and a reflected light from the measurement target, and to output the same as an interference light, wherein the reference surface unit is configured to be replaceable.
