A defect inspecting apparatus includes a first support unit supporting a standard sample having standard defects, a second support unit supporting a wafer having target defects, a light source irradiating an incident light to the standard sample or the wafer, a light receiving part collecting reflection light reflected from the standard sample and the wafer, a detection part detecting the standard defects and the target defects by using the reflection light, a comparing part comparing information obtained using the reflection light reflected from the standard sample with a predetermined standard information of the standard defects to confirm a reliability of a step for detecting the target defects and a determination portion determining whether the step is allowed to be performed or not.