A reticle defect inspection apparatus that can carry out a defect inspection with high detection sensitivity are provided. The apparatus includes an optical system of transmitted illumination for irradiating one surface of a sample with a first inspection light, an optical system of reflected illumination for irradiating another surface of the sample with a second inspection light, and a detecting optical system that can simultaneously detect a transmitted light obtained by the first inspection light being passed through the sample and a reflected light obtained by the second inspection light being reflected by the sample. And the optical system of transmitted illumination includes a focusing lens driving mechanism for correcting a focal point shift of the transmitted light resulting from thickness of the sample.