An apparatus for inspecting a defect, has a light source; a rotating diffuser plate for reducing coherence of light emitted from the light source after its light intensity was adjusted and its illumination range is formed; oscillating mirrors that variably change the beam whose coherence was reduced on a pupil, irradiates it onto a wafer, and forms an image thereof. An image sensor images the wafer by focusing reflected light from the wafer and detects an image signal; a camera observes the detected image; and an image processing unit detects a defect of a pattern formed on the wafer based on the detected image signal. Thus, conditions for illuminating the sample can be changed variably in an arbitrary and easy manner, and a more minute defect can be detected with high sensitivity by changing transmissivity and phase conditions of a pupil filter on the detection side.