A defect inspecting apparatus includes an irradiation optical system having a light source that emits illumination light and a polarization generation part that adjusts polarization state of the illumination light emitted from the light source, a detection optical system having a polarization analysis part that adjusts polarization state of scattered light from a sample irradiated by the irradiation optical system and a detection part that detects the scattered light adjusted by the polarization analysis part, and a signal processing system that processes the scattered light detected by the detection optical system to detect a defect presenting in the sample. The polarization generation part adjusts the polarization state of the illumination light emitted from the light source on the basis of predetermined illumination conditions and the polarization analysis part adjusts the polarization state of the illumination light emitted from the light source on the basis of predetermined detection conditions.