Mask inspection apparatus and mask inspection method

The present invention provides a mask inspection apparatus and method capable of eliminating distortion of each optical image, which is caused by distortions of mirrors and flexure of a mask, and performing a mask inspection with satisfactory accuracy. A stage with the mask held thereon is moved in X and Y directions and an optical image of each pattern written onto the mask is acquired while using the results of measurement by laser interferometers (Step S100). A positional displacement of the acquired optical image is corrected using polynomial equations in which pre-measured amounts of positional displacement of optical images have been fitted (Step S102). Each positional displacement that remains after the polynomial correction is corrected using a map descriptive of pre-measured amounts of positional displacements (S104). Each optical image subsequent to the map correction and a reference image are compared (Step S108).