To provide a defect inspection apparatus for a phase shift mask which is capable of surely detecting the defect, more particularly microdefects of the phase shift mask.

This defect inspection apparatus has light releasing means 13 which releases light of a specific wavelength region, a differential interference optical system 14 which changes the light released from this light releasing means 13 to two beams of light and forms a differential interference image from the edge information indicating the surface shape of the phase shift mask 10 obtained by synthesis of two beams of the reflected light from the surface of the phase shift mask 10, an image detector 15 which converts the differential interference image into an electronic image and a signal processing circuits 16 which compares the output image of this image detector 15 with the reference image obtained by another means, extracts only the specific edge information and defects the defects of the phase shift mask 10.